The aim of the authors in this study was to evaluate the relationships between perceived perinatal stress and social support to psychological health outcomes in mothers. A longitudinal, quantitative study was conducted in Geneva, Switzerland on 235 primiparous mothers from September 2010 to January 2012. Data were collected between gestational weeks 37 and 41 (T1), 2 days post-delivery (T2), and at 6 weeks postpartum (T3). Perinatal stress was associated with depressive symptoms (R(2) = 0.223), anxiety (R(2) = 0.242), and a low sense of parental self-efficacy (R(2) = 0.21). However, satisfaction with social support moderated the relationship of stress to the health of mothers. In particular, the authors noted that the more women were provided with support from their partners, the less depressive symptoms and elevated levels of anxiety they reported, even under stressful conditions, while the satisfaction of support from their mothers boosted their sense of competency. Furthermore, satisfaction with emotional support from professionals tempered the stress during the post-partum period (∆R(2) = 0.032; p < .05). The results revealed that perinatal stress was related to the psychological health of mothers, but social support may modulate these effects. A number of approaches could be implemented to manage this stress.