OBJECTIVE: Diabetes is frequently linked with depression, and both conditions are common complications during pregnancy. However, research findings exploring the relationship between Diabetes Mellitus in Pregnancy (DMP) and Perinatal Depression (PND) have been inconsistent. Thus, this study seeks to examine the association between DMP and PND in a prospective population-based cohort. METHODS: Women aged 18-48 years (n = 4459) were identified from the Biology, Affect, Stress, Imaging and Cognition study. The diagnosis of DMP was based on ICD code O24 from medical records, and was classified as pre-gestational, gestational or unspecified diabetes. PND was assessed using psychometric instruments, clinical interviews and/or register data and categorized into antepartum or postpartum depression. Multivariable logistic regressions were used to study the associations of DMP with antepartum and postpartum depression. RESULTS: Out of 4459 pregnancies, 949 women had antepartum depression (21.2%) and 1123 had postpartum depression (25%). DMP had a prevalence of 1.2%. Women with DMP had two-fold higher odds for postpartum depression compared to women without DMP. While no association was observed between DMP and antepartum depression, women with DMP had more antepartum depressive symptoms compared to those without DMP. None of the types of DMP were associated with antepartum nor postpartum depression. CONCLUSION: Our study shows an association between DMP and PND, which might be considered a risk factor when screening for high-risk groups.