Background: Head circumference (and its related morphologic factors such as head length and width) is one of the morphologic indices that people with autism spectrum disorders (ASD) have different developmental patterns in comparison to their peers. So the aim of this study is to assess head circumference indices in relation to cognitive factors in ASD children and adolescents.

Materials and Methods: In this cross-sectional study, the case group was consisted of 129 students with ASD aged 7-18 years old. The control group was consisted of 103 students with intellectual disability (ID) aged 7-18 years old. Head circumference, head length and width was measured by meter and caliper respectively. In addition, socio- cognitive factors questionnaire was responded by parents.

Results: Results showed that the head circumference, length and width of ASD group was significantly greater than ID group (p<0.001). Moreover, ASD group achieved lower score on SSIS questionnaire than ID group (p<0.001). Furthermore, results showed that in ASD group with increasing the size of head circumference the score on socio-cognitive abilites and skills decreased (p<0.05).

Conclusion: Generally, this study indicated that the developmental trajectory as well as the relation of anthropmetric indices of head circumference and socio-cognitive factors in children and adolescents with ASDs is different from ID population.