Early diagnosing of autism is supposed to rely on behavioral patterns that cannot all be manifested in children before older age. It seems that all diagnostic criteria from DSM/IV and ICD/10 do not apply for children under two years of age and are relevant only for children above this age. The aim of our research has been to reveal the timing of occurrence of diagnostically relevant behaviors as noticed by parents of autistic children.

The sample consisted of 105 parents of autistic children. Questionnaire for appraising the behavioral abnormalities of autistic children provided information on the parents estimation at what age their children started to show these abnormalities.

Deficit in social interactions is first to be noticed by parents (at the child's age of 13–37 months). Problems in communication occur later, at age 18.8–49.5 months. Stereotypic behaviors and interests occur at age of 20.2–34.8 months, the most common being: “plays with toys in an unusual way” (90.6%), and “unusual moving of arms” (80%), observed at age of 2–3.

The most common parents concern are language difficulties, never mind findings that social deficits are observed first (13–37 months). Diagnostic criteria in psychiatric manuals such as ICD-10 or DSM-IV pay little attention to early manifestations of the disturbance. It seems that accurate diagnosis of autism only exceptionally can be made before age 3–4, mostly because diagnostically relevant behaviors do not occur before that age.