The endometrial histology after spontaneous abortion was investigated by performing an endometrial biopsy in the two menstrual cycles subsequent to miscarriage in 12 women. In the first cycle, 66% (8/12) of the biopsies had the following abnormalities: (1) proliferative endometrium (n = 4), (2) proliferative glands and decidualized stroma (n = 1), (3) endometritis (n = 1), and (4) luteal insufficiency (n = 2). In the second cycle, 20% (2/10) of the biopsies demonstrated luteal insufficiency. Forty-five percent (10/22) of the first two cycles after spontaneous abortion demonstrated abnormal endometrial histology, with the first appearing more abnormal than the second (P = 0.06). Two conceptions occurred during the study period; both were uneventful term pregnancies. These findings suggest that a large proportion of the first two menstrual cycles after spontaneous abortion and curettage are abnormal, with the first cycle being more frequently abnormal than the second.