BACKGROUND: The exact molecular and biochemical cause of autism is unknown. Some experts believe that various genetic disorders are linked to autism. This study aimed to evaluate the association between gene polymorphism of vitamin D receptor (VDR) Taq1 (rs 731276) and autism susceptibility and severity in children. METHODS: We enrolled 40 autistic children, and 40 age-gender matched healthy controls. Complete clinical examinations were performed, with a focus on neurological examination, and clinical data from each autistic patient's medical records were reviewed. Polymerase chain reaction-restriction fragment length polymorphism was used to detect Taq1 (rs731276) gene polymorphism in all participants. RESULTS: Males represented 70% of the autistic group and 75% of the control group. The mean age was 5.5±0.5 and 5.6±0.5 years in the autistic, the control groups, respectively. There were significant differences between the autistic and control groups regarding gestational age (p <0.001), family history of psychiatric disorders (p <0.001), and paternal age (p= 0.004). The dominant genotype in the autistic group was the AG (heterozygous) genotype (70%), however, in the control group, the dominant genotype was the AA (wild) genotype (87.5%). There was a significant association between VDR Taq1 (rs731276) genotypes and autism susceptibility (p<0.001). Furthermore, there was no significant association between Taq1 (rs731276) gene polymorphism and the severity of autism (p= 0.138). CONCLUSIONS: Our results reveal a significant association between vitamin D receptor gene polymorphism Taq1 (rs 731276) and autism susceptibility in children, but there is no significant association between this gene polymorphism and the severity of autism.