OBJECTIVE: This study was undertaken to estimate the risk of fetal and maternal complications associated with postterm delivery in Denmark. STUDY DESIGN: A cross-sectional study that used records from the Danish Medical Birth Registry from 1978 to 1993 was performed. All women with registered prolonged pregnancy (n = 78022) and a 5% random sample of all women who gave birth (n = 47021) were linked to the Danish National Discharge Register. We established a postterm group of 77956 singleton deliveries and a term group of 34140 singleton spontaneous deliveries. Logistic regression models were used to analyze data. RESULTS: The risk of perinatal and obstetric complications was high in postterm delivery compared with term delivery (adjusted odds ratios between 1.2 and 3.1). The risk of perinatal death was 1.33 (1.05-1.68). CONCLUSION: Postterm delivery was associated with significantly increased risks of perinatal and maternal complications in Denmark in the period from 1978 to 1993.