OBJECTIVE To study the effects of selective serotonin reuptake inhibitors (SSRIs) on pregnancy outcome. METHODS We performed a population-based study of women exposed to SSRIs during pregnancy (n = 1782). Data were derived from a national project in Finland, established by 3 governmental organizations. In that project, the Drug Reimbursement Register, the Medical Birth Register, the Register of Congenital Malformations, and the Register of Induced Abortions have been linked. Comparisons were made between women with SSRI purchases to matched controls and between women with purchases in different trimesters. Only singleton pregnancies were included. Primary outcomes were major malformations, preterm birth, small for gestational age, low birth weight, and treatment in neonatal special or intensive care unit. Analyses were based on logistic models. RESULTS Major malformations were not more common in infants or fetuses of women with first trimester SSRI purchases (n = 1,398) when compared with controls with no drug purchases (P = .4). Of infants born to mothers with SSRI purchases in the 3rd trimester, 15.7% were treated in special or intensive care unit compared with 11.2% of infants exposed only during the 1st trimester (P = .009, adjusted odds ratio 1.6, 95% confidence interval 1.1-2.2). We found no increased risk of preterm birth (< 37 weeks), birth 32 weeks of gestation or less, small for gestational age, or low birth weight in women with purchases in each trimester or during the 2nd and 3rd trimesters when compared with women with only 1st trimester purchases. CONCLUSIONS Use of SSRIs during pregnancy is not independently associated with increased risk of adverse perinatal outcome other than need for treatment in neonatal special or intensive care unit.