Motivated by the post-war hyperinflation and poor economic conditions of Weimar Germany, Kanner immigrated to the United States in 1924.[2][7] If he had stayed in Austria his fate might have been similar to other Jewish professionals who lost their lives during the war. He stated: "Little did I know, if I had remained in Germany I would have been perished by Hitler in the Holocaust".[1]

When he emigrated to the United States in 1924, he worked at the state hospital in Yankton, South Dakota, where he started his pediatric and psychiatric studies.[4][8] Upon arrival, Kanner was appointed assistant physician at the Yankton State Hospital.[8] It was there Kanner would learn the subtleties of pediatrics and psychiatry, two fields in which he was not experienced. To enhance his command of the English language, Kanner did the crossword puzzles in The New York Times.[9] During his time in South Dakota, Kanner published his first works, which were on general paralysis and syphilis. Kanner also studied the effects of adrenalin on the blood pressure of patients with functional paralysis.[9] Additionally, he published his first book, Folklore of the Teeth, an analysis of dental practices around the world in relation to customs and folklore, in 1928.[10]