Background: Recent research suggests that having a newborn child is associated with substantially reduced risk for maternal suicide. We studied postpartum suicides in a national cohort of mothers and the role of mental disorder, self-harm and delivery related factors. Methods: We used a nested case-control design with data from Swedish registries. The cohort consisted of all women given birth in Sweden 1974–2009. Mothers who died by suicide during follow-up were considered cases (n = 1,786) and risk of suicide was estimated with proximity to delivery as the explanatory variable. In a second step, association between suicide during the first year following delivery (n = 145) and mental disorder, self-harm and delivery related variables risk factors were analyzed. Results: The first postpartum year was associated with a lower risk of suicide, compared to later (RR 0.80, 95%CI 0.66–0.96), which was unaltered after adjustment for socio-economic status and history of self-harm (aRR 0.82, 95%CI 0.68–0.99). Compared to living mothers, suicide victims of the postpartum year more often had affective disorders (aRR 133.94, 95%CI 45.93–390.61), psychotic disorders (aRR 83.69, 95%CI 36.99–189.31) and history of self-harm (aRR 47.56, 95%CI 18.24–124.02). The aRR of stillbirth was 2.66 (95%CI 0.63–11.30). Conclusions: We found only a weak negative association between childbirth during the preceding year and suicide, when using mothers as controls. A severe mental disorder after delivery and a history of self-harm was strongly associated with increased risk of suicide in the postpartum year and may inform the clinical assessment postpartum. [ABSTRACT FROM AUTHOR]