Stephen Hawking was disabled because of amyotrophic lateral sclerosis (ALS), a disease that progressively destroys the nerve cells controlling voluntary movement. He was diagnosed at age 21, while studying at Cambridge, and lived with the condition for 55 years until his death in 2018 at age 76.
What ALS Did to His Body
ALS targets two types of nerve cells: upper motor neurons in the brain and lower motor neurons in the brainstem and spinal cord. These are the cells responsible for every deliberate movement you make, from walking to speaking to swallowing. When they die, the muscles they control stop receiving signals and gradually weaken, shrink, and become paralyzed.
Motor neurons are unusually long cells, some stretching up to a meter from the spinal cord to the muscles they serve. That extreme length makes them vulnerable. The cell has to transport energy-producing structures and essential proteins across that entire distance, and in ALS, that transport system breaks down. Energy production fails at the point where the nerve meets the muscle, the connection degrades, and the muscle loses its nerve supply entirely. Over time, this process spreads from one group of muscles to the next.
What ALS does not destroy is equally important. The disease leaves thinking, vision, hearing, and sensation largely intact. Cognitive decline in ALS does not follow the same pattern as physical disability. Hawking’s intellect remained sharp throughout his life, which is why he could continue producing groundbreaking physics even as his body became almost entirely paralyzed. His mind was, in a real sense, trapped inside a body it could no longer control.
How His Symptoms Progressed
Hawking first noticed problems in the early 1960s as a graduate student at Cambridge. He began experiencing clumsiness, difficulty tying his shoes, and slurred speech. Doctors diagnosed him with ALS (called motor neuron disease in the UK, where he lived) and told him he likely had only a few years to live. The average survival after diagnosis is about 14 months, and most patients die within five years.
His disease progressed, but far more slowly than anyone expected. By the late 1960s he needed a wheelchair. His speech became increasingly difficult to understand, though people close to him could still interpret it. Then in 1985, while traveling in Geneva, he developed pneumonia. The infection was severe enough to require a tracheostomy, a procedure that saved his life but permanently took away his ability to speak.
From that point on, Hawking communicated entirely through technology. A computer program displayed a keyboard on screen, and a cursor scanned across the letters automatically. Hawking selected characters by tensing a single muscle in his cheek, detected by a small infrared sensor mounted on his glasses. A word-prediction algorithm helped speed up the process, but composing even a short sentence was painstakingly slow. The robotic voice that became his trademark was a speech synthesizer connected to this system.
Why He Survived So Much Longer Than Expected
Hawking’s 55-year survival with ALS is one of the longest ever documented, and no single explanation fully accounts for it. His young age at diagnosis is the most significant known factor. Neurologists have found that survival in younger patients is “strikingly better and is measured in many years,” sometimes more than 10, compared to people diagnosed in their 50s or 60s, who have roughly a 50 percent chance of surviving four years.
Still, even among young-onset cases, Hawking was an extreme outlier. His form of the disease progressed unusually slowly, particularly after the first decade. While most ALS patients experience a relatively steady decline, Hawking’s condition seemed to plateau for long stretches. He lost functions in stages: first walking, then fine motor skills, then speech. But the disease never advanced to full respiratory failure on its own, which is what kills most people with ALS. The reasons for this remain unclear, and his case has never been fully explained in medical literature.
What Daily Life Looked Like
By the later decades of his life, Hawking had almost no voluntary movement. He could not feed himself, dress, move his wheelchair without assistance, or perform any basic physical task. He required round-the-clock nursing care. His wheelchair, equipped with a computer and speech synthesizer, became an extension of his body and his primary means of interacting with the world.
As his cheek muscle weakened over the years, even the act of selecting letters became more difficult. Engineers at Intel periodically updated his system to work with less and less physical input. Despite these limitations, Hawking continued to publish scientific papers, give public lectures, write bestselling books, and travel internationally. His disability shaped nearly every aspect of how he lived, but it never stopped his work as a physicist. He produced some of his most important contributions to cosmology and black hole theory decades after losing the ability to hold a pen.