I don't know what to say when the one of the most prolific science fiction writers in the world finds out he has early onset Alzheimer's disease
The writer, 59, who gave the news on the website of Discworld artist Paul Kidby, said the condition was behind a "phantom stroke" earlier this year.
Discworld author Pratchett has sold more than 55 million books worldwide.
He said in a statement that with forthcoming conventions and the need to inform his publishers it would have been "unfair to withhold the news".
Author Terry Pratchett is suffering from a rare form of early Alzheimer's disease, it has been revealed.
suffering from a rare form of early Alzheimer's disease, it has been revealed.
"I will, of course, be dead at some future point, as will everybody else," he said.
"I know it's a very human thing to say 'is there anything I can do', but in this case I would only entertain offers from very high-end experts in brain chemistry."