To examine whether recurrent spontaneous abortion (RSA) can be distinguished from repeated sporadic spontaneous abortion, the clinical course of 38 cases with three or more consecutive and unexplained first trimester RSAs were retrospectively investigated in this study. For comparison with controls, the clinical course was examined of 38 fertile females, who had had sporadic abortions. In 19 (50%) RSAs and 6 (16%) controls, fetal cardiac activity was demonstrated by ultrasound during the course of pregnancy. The rate of detection of live fetus during pregnancy or at 8 weeks +/- 7 days gestation, was significantly greater in the RSA group compared to the control. The rate of vaginal bleeding before spontaneous abortion was significantly less in the RSA group than in the control group. There was no difference between the two groups in age or gestational age at spontaneous abortion. The patients with RSA were all examined for antiphospholipid antibodies in their sera and these were detected in eight of them. However, there was no difference in the rate of positive fetal cardiac activity between the RSA patients who tested positive or negative for antibody. These results reveal that the clinical course of RSA is very different from the course of sporadic abortion. Although sporadic abortion is a common complication of pregnancy, RSA is not a random repeated abortion, but rather a separate disease from sporadic abortion in normal fertile females.