During the years 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 were found to have grade I placenta previa (PP), 12 to have grade II, 14 to have grade III, and 9 patients to have grade IV PP. These different variants of PP were correlated with the ultimate outcome of these 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 those patients who had grades III and IV PP, 13 out of 23 had premature or immature deliveries. These results suggest that finding of MTPP, especially symptomatic MTPP, should alert the physician to the clinical significance of PP later in pregnancy.