INTRODUCTION: Compared with the general population, women with diabetes are at increased risk of various adverse perinatal outcomes. The objective of this study is to examine associations between type of maternal insurance and peripartum and fetal outcomes in women with pregestational type 1 diabetes mellitus (DM). METHODS: Retrospective cohort study of 2,082 singleton births among women with type 1 DM in California from 2005 to 2008. Maternal insurance status was classified as Medicaid or private insurer. Statistical analysis included χ2 tests and multivariable logistic regressions. RESULTS: Compared with women with private insurance, women with Medicaid insurance had a higher prevalence of adverse peripartum and neonatal outcomes in bivariate analysis. Medicaid-insured patients had a higher prevalence of intrauterine fetal demise (2.9% compared with 1.2%, P=.005), fetal anomalies (14.8% compared with 10.1%, P=.001), small for gestational age (7.5% compared with 4.6%, P=.005), and large for gestational age (16.3% compared with 20.0%, P=.030). Preterm births less than 28 weeks of gestation were significantly higher in those with Medicaid insurance (2.3% compared with 1.1%, P=.035); however, this finding was not statistically significant when looking at preterm births less than 37 or 32 weeks of gestation. In multivariate analysis controlling for age, race, chronic hypertension, nulliparity, and number of prenatal care visits, fetal anomalies (adjusted odds ratio [OR] 1.5, 95% confidence interval [CI] 1.11–2.10) and intrauterine fetal demise (adjusted OR 2.8, 95% CI 1.0–8.1) remained statistically significant. CONCLUSION: Perinatal outcomes among women with type 1 DM differ by insurance status with a higher prevalence of adverse outcomes observed in women with type 1 DM with Medicaid insurance compared with private insurance.