BACKGROUND The relationship between small for gestational age (SGA) and autism spectrum disorders (ASDs) remains unknown. OBJECTIVE This meta-analysis aimed to investigate the relationship between SGA and the risk of ASD. METHODS We searched PubMed, Web of Science, and Scopus databases from inception to November 2020. The heterogeneity across studies was explored using the I2 statistic. The possibility of publication bias was assessed using Begg test. The results were reported using the odds ratio (OR) and 95% confidence interval (CI) using a random-effects model. RESULTS The literature search yielded 824 articles with 8,752,138 participants. We assessed the association between SGA and the risk of ASD in cohort and case-control studies. Based on the random-effects model, compared with SGA, the estimated OR of the risk of ASD was 1.17 (95% CI, 1.09-1.24). Therefore, there was a significant association between SGA and the risk of ASD. CONCLUSIONS Based on OR reports in epidemiological studies, we showed that SGA is a risk factor for and can increase the risk of ASD. The association between SGA and ASD risk has further relevance to the current public health emphasis on appropriate prepregnancy weight and pregnancy weight gain.