This paper examines the genesis of Leo Kanner’s 1943 seminal paper on autism. It shows that describing children as autistic or lacking affective contact with people was not new by this time. But Kanner’s proposal that infantile autism constituted a hitherto unidentified condition that was inborn and different from childhood schizophrenia was new. It also shows that Georg Frankl’s influence on Kanner was important, but Kanner did not misappropriate his ideas or his research. Kanner developed his views on the basis of his observations of several children, his knowledge of the literature on childhood conditions, and his interactions with many scholars.