Background: Autism Spectrum Disorder (ASD) is a life -long neurodevelopmental disorder and significantly influences the quality of life in children. The screening of ASD in children aged between 16-30 months to early detection and early intervention for better prognosis. Methods: This cross-sectional study was conducted in the southwest of Iran (Yasuj) with dominant Lore ethnicity in 2017. A total of 1504 mother- child pairs with children aged between 16-30 months were selected through simple random sampling from the integrated national health system as the framework. ASD screening was implemented using the Modified checklist for autism in toddlers- revised, with follow-up interview (M-CHAT-R/F). Demographic data such as sex of children, and parental age at their time of pregnancy were collected for all children. Results: Risk of ASD was low, moderate and high in 1447 (96.2%), 54 (3.6%) and 3 (0.2%) in screening, respectively. The estimated rate of ASD prevalence was 80 per 10000 (12 out of 1504) or 1 in 125. Mother's age ≥35 ( P value = 0.002, OR = 11.65, CI 95% : 2.49-54.35) and father's age ≥40 ( P value = 0.0001, OR = 19.64, CI 95% : 4.89-78.82) were predicting factors of ASD in toddlers aged 16-30 months. Conclusions: Given that, increasing the age of marriage in Iran and recent trend towards delayed childbearing; children born to older parents are at a higher risk for having ASD. So, increasing the public awareness is necessary.