During 1974-1977 ultrasonic placentography demonstrated midtrimester placenta previa (MTPP) in 123 women. The procedure was performed because of vaginal bleeding in 65 cases and prior to amniocentesis in 58 asymptomatic cases. Eighty-eight patients had grade I placenta previa (PP), 12 had grade II, 14 had grade III and 9 patients had grade IV PP. These different variants of PP were correlated with the ultimate outcome of the pregnancies. Bleeding due to PP or PP at term were reasons for cesarean section in 4 cases of grade I PP in 2 cases of grade II, in 7 cases of grade III and in 7 out of 9 cases of grade IV PP. Among patients who had grades III and IV PP, 13 out of 23 had premature or immature deliveries. The finding of MTPP, especially symptomatic MTPP, should alert the physician to the clinical significance of PP later in pregnancy.