The risk for a clinical spontaneous abortion in a pregnancy following 0 to 4 consecutive spontaneous abortions was estimated in a large, unselected, Danish population, including approximately 300,500 pregnancies. The overall risk for spontaneous abortion was 11% and the risk for a spontaneous abortion was 16, 25, 45 and 54% after 1 to 4 previous consecutive spontaneous abortions, respectively. For women over 35 years, the risk for spontaneous abortion was significantly increased, but the almost identical abortion rates after repeated abortions in both young and old women indicate a risk factor which is not age-related.