Objective. To study the incidence trends of placental abruption. Design. Register-based retrospective study. Setting. The Finnish Medical Birth Register and Hospital Discharge Register. Population. A total of 6231 placental abruption cases among 1 576 051 deliveries. Methods. Data on demographic and pregnancy and delivery associated outcomes were collected. Data on overall incidence and maternal age were available 1980–2005. Data on other variables were available 1987–2005. Main outcome measure. Placental abruption Results. The overall incidence of placental abruption was 395/100 000 (0.4%). The incidence decreased 31%, from 487/100 000 in 1980 to 337/100 000 in 2005 (p < 0.001). The incidence was lowest among women aged 20–24 years (305/100 000) and highest among women aged ≥45 years (1309/100 000). During 1987–2005 the incidence was lowest among women with one or two deliveries (353/100 000) and highest in nulliparous women (382/100 000) and in women with three or more deliveries (595/100 000). The incidence was nearly double (577/100 000) among smoking compared with non-smoking women (341/100 000). The incidence was highest between gestational weeks 26 and 29. Among newborns weighing <1500 g the incidence was higher (5734/100 000) than among those weighing ≥2500 g (251/100 000). The incidence was higher in multiple (903/100 000) than in singleton pregnancies (374/100 000). Conclusion. The incidence of placental abruption decreased during 1980–2005. The incidence was highest among women aged 45 years or more, multiparous and smoking women, in multiple pregnancies and in women with low birthweight newborns.