There is no concrete evidence to suggest that Isaac newton had autism as we understand it today. While Newton did exhibit certain behaviors that are sometimes associated with autism, it is important to remember that diagnosing historical figures based on modern criteria may not be accurate.
Some people suspect that he did have Asperger's Syndrome, while others think it is unlikely. Isaac Newton lived before the condition of Asperger's Syndrome was identified, so speculation is based on some known aspects of his life. Most people have some behaviors that occur in people with Asperger's Syndrome, so it is difficult to identify people in the past who have had autism or Asperger's Syndrome unless they described their difficulties in diaries or were seeing doctors who documented their unidentified conditions.
Sir Isaac Newton did indeed keep a personal diary, and I know of at least one biography of Newton that has used information from his diary to shed light on questions about his personality and feelings. There is no shortage of information about Newton that can be, and has been, used by biographers and historians and psychiatrists who have researched Newton and written about Newton. The main reasons why we might have difficulty in judging whether or not Newton was autistic are the lack of precision in the diagnostic criteria for conditions such as Asperger syndrome, and a lack of detailed information about Newton in his early childhood, but we do know that throughout his life Newton displayed personality and cognitive traits that were consistent with having Asperger syndrome or autism.
Many biographies of Newton have been written over the years - by authors such as James Glieck, Richard Westfall and Frank Manuel. There is also a large body of literature about famous people who are thought to have had autism or Asperger syndrome (AS), which discusses Newton as a case of Asperger syndrome or autism. Please find below a list of references that discuss Newton with regard to the autistic spectrum. You will find arguments in this reading list for and against the proposition that Newton had AS.
The list of references below is an excerpt from the list of 155 famous people who have Asperger syndrome/autism or might have had Asperger syndrome/autism, which is published at the blog Incorrect Pleasures, which can easily be found by Googling the name of the blog. It is a very large and carefully researched list, which could be used as a starting point for more detailed research.
Junior Books
Elder, Jennifer and Thomas, Marc (Illustrator) (2005) Different like me: my book of autism heroes. Jessica Kingsley, 2005.
[Newton and many other famous people are profiled in this book for a junior readership which was written by the mother of an autist]
Krull, Kathleen (2006) Isaac Newton. (illustrated by Boris Kulikov), Viking, 2006.
[junior biography in the Giants of Science series, Asperger syndrome discussed]
Adult Books and Articles
Baron-Cohen, Simon (2003) The essential difference.Penguin Books.
[some discussion of Newton in this book about Asperger syndrome]
Fitzgerald, Michael (2006) Autism, Asperger's syndrome and creativity. Autism2006: AWARES Conference Centre. October 4th 2006.
http://212.74.184.44:8083/BM_DIRECTORY/E/BM000001662/7679/FIT1.PDF
http://awares.nemisys.uk.com/conferences/show_paper.asp?section=000100010001&conferenceCode=000200020002&id=42
[many famous people discussed including Newton]
Fitzgerald, Michael and James, Ioan (2007) The mind of the mathematician. Johns Hopkins University Press, 2007.
[many famous people discussed including Newton]
Fitzgerald, Michael, and O'Brien, Brendan (2007) Genius genes: how Asperger talents changed the world. Autism Asperger Publishing Company, 2007.
[many famous people discussed including Newton, parts of this book available to read free through Google Book Search]
James, Ioan (2005) Asperger syndrome and high achievement: some very remarkable people. Jessica Kingsley Publishers, 2005.
[includes a chapter about Newton]
James, Ioan (2004) Remarkable physicists: from Galileo to Yukawa. Cambridge University Press.
[Newton, Cavendish, Einstein and Dirac identified as autistic, but not discussed as autists]
James, Ioan (2003) Singular scientists. Journal of the Royal Society of Medicine. January 2003. Vol. 96, number 1, p. 36-39.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12519805
[Irene Joliot-Curie, J. M. W. Turner, Paul Dirac, Bela Bartok, Wittgenstein, Cavendish, Newton, Einstein]
Keynes, Milo (2008) Balancing Newton's mind: his singular behaviour and his madness of 1692-93. Notes & Records of the Royal Society. 20th September 2008 vol. 62 no. 3 p.289-300.
http://rsnr.royalsocietypublishing.org/content/62/3/289.full
[The author argues that Newton's suspicious personality was caused by separation from his mother in early childhood and was not caused by AS, full text of paper available free online]
Royal College of Psychiatrists (2006) Royal College of Psychiatrists Annual Meeting 2006 Glasgow: Thatcherism founder had Asperger's Syndrome. (press release) The Royal College of Psychiatrists. 11th July 2006.
http://www.rcpsych.ac.uk/pressparliament/pressreleases2006/pr820.aspx
[Sir Keith Joseph, Enoch Powell, Eamon de Valera, W. B. Yeats, Sir Isaac Newton]
Sacks, Oliver (2004) Autistic geniuses?: we're too ready to pathologize (letter). Nature. May 20th 2004, Vol. 429, p. 241.
[a letter in which Sacks states that he does not believe that Wittgenstein, Einstein nor Newton "were significantly autistic"]
Sacks, Oliver (2002) Uncle Tungsten: memories of a chemical boyhood. Picador, 2002.
[in the notes from page 119-121 Sacks discusses Henry Cavendish, describing him as an "autistic genius" while diagnosing Newton with "neurosis" rather than autism]
Yes, Isaac Newton had indeed suffered from a mental illness. He was a great mathematician of the 17th century and had been diagnosed with and suffered from nervous breakdowns, some say Bipolar disorder, and perhaps anxiety problems. There are many famous roles in our past that have suffered from mental illnesses. One is Vincent Van Gogh who had suffered from clinical/manic (I forget which) depression and bipolar disorder. That doesn't make them different from others, though. They're all the same. Just a little bit more creative. ;)
Isaac Newton formulated the laws of motion. These should not be confused with the laws of planetary motion by Keplar
Isaac Newton the Elder, Iaac Newton was named after his father.
Isaac Newton and Hannah Newton were siblings. Hannah Newton was Isaac Newton's younger half-sister.
No, Isaac Newton was not Canadian. He was English.
Isaac Newton's father was also named Isaac Newton, but his mother's name is not well-documented in historical records.
Sir Isaac Newton.
Hannah Ayscough
Isaac Newton formulated the laws of motion. These should not be confused with the laws of planetary motion by Keplar
Sir Isaac Newton did not have a nickname. He was simply known as Sir Isaac Newton during his lifetime.
Isaac's father was also named Isaac newton.
"Isaac Newton was Sit Isaac Newton's real name.
Isaac Newton Clark has written: 'Isaac Newton Clark'
Isaac Newton the Elder, Iaac Newton was named after his father.
Isaac Newton
Isaac newton
Isaac Newton and Hannah Newton were siblings. Hannah Newton was Isaac Newton's younger half-sister.
Isaac newton discovered the law of gravity.