Background. Recent evidence suggests that postpartum psychiatric episodes may share similar etiological mechanisms with immune-related disorders. Pre-eclampsia is one of the most prevalent immune-related disorders of pregnancy. Multiple clinical features are shared between pre-eclampsia and postpartum psychiatric disorders, most prominently a strong link to first pregnancies. Therefore, we aimed to study if pre-eclampsia is a risk factor for first-onset postpartum psychiatric episodes. Method. We conducted a cohort study using the Danish population registry, with a total of 400 717 primiparous women with a singleton delivery between 1995 and 2011. First-lifetime childbirth was the main exposure variable and the outcome of interest was first-onset postpartum psychiatric episodes. The main outcome measures were monthly incidence rate ratios (IRRs), with the period 11-12 months after birth as the reference category. Adjustments were made for age, calendar period, reproductive history, and perinatal maternal health including somatic and obstetric co-morbidity. Results. Primiparous women were at particularly high risk of first-onset psychiatric episodes during the first month postpartum [IRR 2.93, 95% confidence interval (CI) 2.53-3.40] and pre-eclampsia added to that risk (IRR 4.21, 95% CI 2.89-6.13). Having both pre-eclampsia and a somatic co-morbidity resulted in the highest risk of psychiatric episodes during the 3-month period after childbirth (IRR 4.81, 95% CI 2.72-8.50). Conclusions. We confirmed an association between pre-eclampsia and postpartum psychiatric episodes. The possible explanations for this association, which are not mutually exclusive, include the psychological impact of a serious medical condition such as pre-eclampsia and the neurobiological impact of pre-eclampsia-related vascular pathology and inflammation.