The number of reported autistic children has increased dramatically since the 1970s, especially in Western countries. Similarly, it was observed that there was a gradual increase in the number of children with Autism Spectrum Disorder (ASD) in the behavioral medicine clinic (SQUH). Since there are no previous studies have been done on prevalence of ASD in Oman, we conducted this study to explore the prevalence of ASD in Oman. Moreover, we are interested to identify the symptoms and signs (characteristics) of autistic children. We also aim to measure the degree and extent of association between ASD and the leading risk factors. We used case-control study to achieve our purposes; we selected 260 subjects (130 cases and 130 controls). About 70% of the information was obtained from the parents through telephone interview; the remainder was obtained through face to face interview and self-administered. Chi-square and odds ratio were used to find the association between ASD and various characteristics under study with p-value less than or equal to 0.05 as a significant level of association. Logistic regression and multivariate analysis were used to adjust for confounding variables. Because there has been no treatment for ASD till now but there is an ability to treat the symptoms, we described some characteristics in 130 autistic cases to identify the common symptoms for treatment purpose. We also calculated the prevalence of ASD among children aged 0 -14 years in Oman. The results of crude analysis of the study showed that among demographic risk factors advanced father's age > 49 years (OR=3.81, 95% CI 1.14, 12.68) and mother education (P-value=0.006) were positively associated with the increased risk of ASD. A child's sex was a risk factor of ASD because boys were more likely to get ASD as compared to girls by the ratio 3:1. Among those women who had problems during pregnancy period like psychological stress and social problems were positively associated with the increased risk of ASD (OR= 3.20, 95% CI 1.30, 7.85). Breast feeding was found to be a protective way from ASD and it was positively associated with ASD (OR= 3.50, 95% CI 1.11, 11.04). Among those autistic children who had someone from their relatives affected with the same disorder were positively sorteon associated with ASD (OR=2.90, 95% CI 1.10, 7.67). In addition, Families who have one child with ASD had an increased risk of having another child with the same disorder. After adjustment for possible confounding factors which were nationality of the participants, place of living, mother educational level and monthly family income, approximately the same results were obtained. That means the confounding factors did not have that much impact on our study. After we applied multivariate analysis by using logistic regression (backward step-wise method) for all risk factors under study, we concluded that there were three main risk factors associated with the increased risk of ASD. These factors were advanced father's age, psychological stress and social problems during pregnancy and breast feeding period.