The aim of the present study was to identify obstetrical factors predicting sepsis neonatorum following a full-term pregnancy. In 1982 26 infants out of 2,977 full-term pregnancies had septicemia. For comparison 42 women of corresponding age were randomly selected. A stepwise regression analysis was performed in order to evaluate the association between seven different variables and sepsis neonatorum. We found that prolonged rupture of the membranes (p less than 0.003) and primary amniotomy (p less than 0.02) were the most important factors predicting sepsis neonatorum (r2 = 0.22). Factors such as cervical ripening, vaginal examinations, intrauterine monitoring devices, prolonged labor and prolonged pregnancy did not add to the predicted power of the analysis.