The cause was cancer, said Kate Edgar, his longtime personal assistant.
Dr. Sacks revealed in February that an earlier melanoma in his eye had spread to his liver and that he was in the late stages of terminal cancer.
As a medical doctor and a writer, Dr. Sacks achieved a level of popular renown rare among scientists. More than 1 million copies of his books are in print in the United States, his work was adapted for film and stage, and he received about 10,000 letters a year.
Dr. Sacks variously described his books and essays as case histories, pathographies, clinical tales, or "neurological novels." His subjects included Madeleine J., a blind woman who perceived her hands only as useless "lumps of dough"; Jimmie G., a submarine radio operator whose amnesia stranded him for more than three decades in 1945; and Dr. P. — the man who mistook his wife for a hat — whose brain lost the ability to decipher what his eyes were seeing.
Describing his patients' struggles and sometimes uncanny gifts, Dr. Sacks helped introduce syndromes like Tourette's or Asperger's to a general audience. But he illuminated their characters as much as their conditions; he humanized and demystified them.
In his emphasis on case histories, Dr. Sacks modeled himself after a questing breed of 19th-century physicians, who well understood how little they and their peers knew about the workings of the human animal and who saw medical science as a vast, largely uncharted wilderness to be tamed.
"I had always liked to see myself as a naturalist or explorer," Dr. Sacks wrote in "A Leg to Stand On" (1984), about his own experiences recovering from muscle surgery. "I had explored many strange, neuropsychological lands — the furthest Arctics and Tropics of neurological disorder."
He was also a man of contradictions: candid and guarded, gregarious and solitary, clinical and compassionate, scientific and poetic, British and almost American.
"In 1961, I declared my intention to become a United States citizen, which may have been a genuine intention, but I never got round to it," he told The Guardian in 2005.
Dr. Sacks first won widespread attention in 1973 for his book "Awakenings," about a group of patients with an atypical form of encephalitis at Beth Abraham Hospital in the Bronx. When Dr. Sacks started his clinical career there, in 1966, many of the patients had been catatonic, locked inside themselves for decades as a result of their "sleeping sickness."
Dr. Sacks gave them the drug L-dopa, which was just beginning to be recognized as a treatment for similar symptoms in patients with Parkinson's, then watched as they emerged into a world they did not recognize. Some responded better than others — both to the drug and to their changed circumstances — and Dr. Sacks used his book to explore the differences and celebrate his patients' limited rebirth.
"I love to discover potential in people who aren't thought to have any," he told People magazine in 1986.
The Independent of London called Dr. Sacks "the presiding genius of neurological drama." Reviewers praised his empathy and his graceful prose. Scientists could be dismissive, however, complaining that his clinical tales put too much emphasis on the tales and not enough on the clinical. A London neuroscientist, Ray Dolan, told The Guardian in 2005: "Whether Dr. Sacks has provided any scientific insights into the neurological conditions he has written about in his numerous books is open to question. I have always felt uncomfortable about this side of this work, and especially the tendency for Dr. Sacks to be an ever-present dramatis persona."
In an otherwise laudatory review of "The Man Who Mistook His Wife for a Hat" in The New York Times Book Review, the neuropsychologist John C. Marshall took issue with what he saw as Dr. Sacks' faux-naïve presentation ("He would have us believe that an experienced neurologist could fail to have read anything about many of the standard syndromes"), and called his blend of medicine and philosophy "insightful, compassionate, moving and, on occasion, simply infuriating."
A skilled pianist, Dr. Sacks often wrote about the relationship between music and the mind, eventually devoting a whole book, "Musicophilia" (2007), to the subject. He disagreed with the Harvard psychologist and author Steven Pinker's view of music as "auditory cheesecake, an evolutionary accident piggybacking on language," and pointed to its ability to reach dementia patients as evidence that music appreciation is hard-wired into the brain.
"I haven't heard of a human being who isn't musical, or who doesn't respond to music one way or another," he told an audience at Columbia University in 2006. "I think we are an essentially, profoundly musical species. And I don't know whether — for all I know, language piggybacked on music."
Oliver Wolf Sacks was born in London, the youngest of four sons of Samuel Sacks and the former Muriel Elsie Landau, who were both doctors. His father, in Dr. Sacks' words a "moderately Orthodox" Jew, read the Bible daily, and Dr. Sacks often demonstrated a spiritual impulse in his books. But in "Uncle Tungsten," his 2001 memoir about his childhood love of chemistry, he said that the inflamed Zionist meetings his parents held before the war helped turn him away from organized religion.
After receiving his medical degree from the Queen's College, Oxford, Dr. Sacks moved to America in the early 1960s for an internship at Mount Zion Hospital in San Francisco, then did his residency at the University of California, Los Angeles. He embraced the culture he found in California — befriending the poet Thom Gunn, entering weight-lifting competitions, and joining the Hells Angels on motorcycle trips to the Grand Canyon, adventures he wrote about in his 2015 memoir, "On the Move: A Life."
In that book, he also discussed his sexual identity for the first time, describing his adolescent realization that he was gay. After several early flings, he wrote, he settled into a period of celibacy that lasted 35 years before he found love late in life. He leaves his partner of six years, writer Bill Hayes.
Dr. Sacks remained active well into his later years. In 2007, at 74, he severed his 42-year relationship with the Albert Einstein College of Medicine to accept an interdisciplinary teaching position at Columbia. In 2012, he returned to the New York University School of Medicine as a professor of neurology. And despite the enormous success of his books, he never gave up his unglamorous medical practice — partly, no doubt, because it provided him with material, but also because he genuinely loved working with patients.
In 1989, interviewing him for "The MacNeil/Lehrer NewsHour," Joanna Simon asked Dr. Sacks how he would like to be remembered in 100 years.
"I would like it to be thought that I had listened carefully to what patients and others have told me," he said, "that I've tried to imagine what it was like for them, and that I tried to convey this.
"And, to use a biblical term," he added, "bore witness."
He also bore witness to his own dwindling life, writing reflective essays even in his last days. On Aug. 10, his assistant, Edgar, who described herself as his "collaborator, friend, researcher, and editor" as well, wrote in an e-mail: "He is still writing with great clarity. We are pretty sure he will go with fountain pen in hand."
Several days later, a valedictory essay titled "Sabbath" appeared in The New York Times. In it, Dr. Sacks considered the importance of the Sabbath in human culture and concluded:
"And now, weak, short of breath, my once-firm muscles melted away by cancer, I find my thoughts, increasingly, not on the supernatural or spiritual, but on what is meant by living a good and worthwhile life — achieving a sense of peace within oneself. I find my thoughts drifting to the Sabbath, the day of rest, the seventh day of the week, and perhaps the seventh day of one's life as well, when one can feel that one's work is done, and one may, in good conscience, rest."