This study was conducted to develop a behavioral checklist to predict an autistic disorder and to identify the earliest detecting time.

One hundred and fifty eight children including normal, autistic, institutionalized normal, and retarded were assessed using critical interaction behavioral markers from literature review. Data was collected by semi-structured mother-child interaction by videotape recording and analyzed by factor analysis, Cronbach α, Kappa, χ², and Duncan.

Ten behavioral markers were sorted into 2 factors; joint-attention and synchronized behavior. Autistic children were impaired in pretend play, prodeclarative pointing, proimperative pointing, gaze-monitoring, referential looking, showing, joint-attention, rhythmical vocal exchange, and synchronized laughing. The sychronized behavior was also a critical marker to predict the autistic disorder. However, it was difficult to differentiate autistic disorder from mental retardation. In addition, the appropriate detecting time was around 18 months after birth.

This checklist should be behavior markers to predict autistic disorder and could be useful as educational material at children's clinics, parents class, and for caregivers in the health center. In addition, early detection should lead to treatment being started as soon after 18 months of age as possible.