We performed a systematic literature search regarding maternal diabetes before and during pregnancy and the risk of autism spectrum disorders (ASD) in the offspring. Of the 178 potentially relevant articles, 12 articles including three cohort studies and nine case-control studies were included in the meta-analysis. Both the meta-analyses of cohort studies and case-control studies showed significant associations. The pooled relative risk and 95% confidence interval (CI) among cohort studies was 1.48 (1.25-1.75, p < 0.001). For case-control studies, the pooled odds ratio and 95% CI was 1.72 (1.24-2.41, p = 0.001). No indication of significant heterogeneity across studies or publication bias was observed. In conclusion, maternal diabetes was significantly associated with a greater risk of ASD in the offspring.