OBJECTIVE: To identify the incidence, risk factors, and maternal and neonatal outcome of pregnancies with abnormal placentation at a single center. STUDY DESIGN: A retrospective review of the medical records of the deliveries in 1999-2003 at the Department of Obstetrics, University Hospital Zurich, was conducted with respect to abnormal placentation, and the incidence, risk factors and outcomes were observed. RESULTS: Thirty-one women with abnormal placentation were identified. They represented 0.31% of deliveries during the 5-year period. The significant factors associated with abnormal placentation were previous uterine curettage (OR = 19.3, 95% CI 11.6-32.3), previous uterine surgery other than cesarean sections (OR = 49.6, 95% CI 24.3-102.3) and coexistent placenta previa (OR = 16.1, 95% CI 4.7-43.7). No case of maternal death occurred, and 1 neonatal death due to uterine rupture occurred in the study group. CONCLUSION: The most important risk factor in abnormal placentation was a previous uterine intervention.