Hawking is a victim of amyotrophic lateral sclerosis (ALS), a form of motor neurone disease which attacks the nerves that controls voluntary movement.
When he was asked about the idea of assisted suicide, Hawking said: "I think those who have a terminal illness and are in great pain should have the right to choose to end their lives and those that help them should be free from prosecution. We don't let animals suffer, so why humans?"
Source: Medindia