This study aims to prospectively examine peripartum changes in social support in women with and without anxiety and depressive disorders prior to pregnancy. Data come from the Maternal Anxiety in Relation to Infant Development (MARI) Study, a prospective-longitudinal investigation among n = 306 expectant mothers. DSM-IV anxiety and depressive disorders were assessed in early pregnancy using the Composite International Diagnostic Interview for Women (CIDI-V). Social support was assessed with the Social Support Questionnaire during pregnancy as well as 4 and 16 months postpartum. Perceived social support in the total sample declined from prepartum to postpartum. Levels of prepartum and postpartum social support were lower in women with comorbid anxiety and depressive disorders compared to those with pure depressive disorder(s), pure anxiety disorder(s), or comorbid anxiety and depressive disorders prior to pregnancy. Moreover, social support more strongly declined from prepartum to postpartum in women with comorbid anxiety and depressive disorders compared to those without anxiety and depressive disorder prior to pregnancy. Findings suggest that women with a previous history of comorbid anxiety and depressive disorders are at particular risk for deficient social support during pregnancy and after delivery and might thus profit from targeted early interventions.