Nogle tilstande kan have symptomer, der ligner autisme, og derfor skal fagfolk være omhyggelige, når de skal stille en diagnose og behandle den.
Følgende er en liste over beslægtede syndromer/lidelser, der manifesterer adfærd, der ligner autisme og/eller er mere udbredt hos personer med autisme:
Congenital Rubella Syndrome: Helen Keller National Center for Deaf-Blind Youths and Adults
Cornelia deLange Sydrome: Cornelia deLange Syndrome Foundation
Down Syndrome: Cornelia deLange Syndrome Foundation
Down Syndrome: National Down Syndrome Society
Fragile X Syndrome: National Down Syndrome Society
Fragile X Syndrome: National Fragile X Foundation
Klüver-Bucy Syndrome: National Fragile X Foundation
Klüver-Bucy Syndrome: National Fragile X Foundation: National Institute of Neurological Disorders and Stroke
Landau-Kleffner Syndrome: National Institute of Neurological Disorders and Stroke
Landau-Kleffner Syndrome: National Institute of Neurological Disorders and Stroke National Institute of Neurological Disorders and Stroke
Lesch-Nyhan Syndrome: National Institute of Neurological Disorders and Stroke
Lesch-Nyhan Syndrome: National Institute of Neurological Disorders and Stroke Lesch-Nyhan Disease network
Ubehandlet Phenylketonuria (PKU): Lesch-Nyhan Disease network
Untreated Phenylketonuria (PKU): National PKU Alliance
Prader-Willi syndrom: National PKU Alliance
Prader-Willi Syndrome: Prader-Willi Syndrome Association
Rett Syndrome: International Rett Syndrome Foundation
Tourette Syndrome: Tourette Syndrome Association
Tubersklerose: Tourette Syndrome Association
Tubersklerose: Tuberous Sclerosis Alliance
Williams Syndrome: Williams Syndrome: Williams Syndrome Association
Selv om autisme almindeligvis opfattes som en psykisk lidelse, er det en helkropstilstand og kan manifestere sig gennem en række fysiske symptomer og karakteristika.