Aim: To study the knowledge and attitude of family medicine residents about autism spectrum disorder in postgraduate programs of family medicine in western region, Saudi Arabia. Methods: This cross-sectional study was conducted from January to February 2020 in Al-Madinah, Saudi Arabia. The data were collected through an online questionnaire. Results: Out of 246 family medicine residents, 126 (52.0%) were female, with average age 28.3 (3.1), 91 (37.0%) were R4 and 65 (26.4%) were R3, 112 (45.5%) encountered cases of autism, 13 (5.3%) attend training program, and 38 (15.4%) reported family history of autism. The mean knowledge score was 12.8 indicating average level of knowledge, where 99 (40.2%) had moderate level of knowledge, 79 (32.1%) had poor knowledge, and 68 (27.6%) had good knowledge, 33 (13.4%) had an awareness about specialized Centre for autism in Saudi Arabia, half of the residents had positive attitude towards autism, A significant highest score was found among those who were in higher level of residency (p=0.003), and those who didn’t have a family history of autism (p=0.026). Conclusion: Family medicine residents showed average level of knowledge and attitude dealing with autism patients. Were, less than tenth attend training program in child mental health. and less than fifth had an awareness about specialized Centre for autism in Saudi Arabia. Recommendation: Decision makers and administrators in colleges and universities requested to give more attention to improve psychiatry curriculum including autism subject.