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Abstract: Objective: The aim of this study was to investigate the relationship between autism spectrum disorder (ASD) and general vaccinations, including measles–mumps–rubella (MMR) vaccine, in Japanese subjects, a population with high genetic homogeneity. Patients and methods: A case–control study was performed. Cases (n =189) were diagnosed with ASD, while controls (n =224) were volunteers from general schools, matched by sex and birth year to cases. Vaccination history and prenatal, perinatal, and neonatal factors from the Maternal and Child Health handbook, which was part of each subject''s file, were examined. To determine the relationship between potential risk factors and ASD, crude odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated, and the differences in mean values of the quantitative variables between cases and controls were analyzed using an unpaired t-test. Moreover, MMR vaccination and the effect of the number of vaccine injections were investigated using a conditional multiple regression model. Results: For MMR vaccination, the OR was 1.04 (95% CI, 0.65–1.68), and no significant differences were found for the other vaccines. For all of the prenatal, perinatal and neonatal factors, there were no significant differences between cases and controls. Furthermore, regarding the presence of ASD, MMR vaccination and the number of vaccine injections had ORs of 1.10 (95% CI, 0.64–1.90) and 1.10 (95% CI, 0.95–1.26), respectively, in the conditional multiple regression model; no significant differences were found. Conclusions: In this study, there were not any convincing evidences that MMR vaccination and increasing the number of vaccine injections were associated with an increased risk of ASD in a genetically homogeneous population. Therefore, these findings indicate that there is no basis for avoiding vaccination out of concern for ASD. [Copyright &y& Elsevier]