Epidemiologic studies, retrospective and prospective, were done on 1500 abortions collected from 1966-1972. No secular or seasonal variations were observed. From the analysis of the relative frequencies of the different types of chromosome anomalies it is estimated that 1 out of every 2 conceptions has a chromosome anomaly. Maternal-age influence was found only for the autosomal trisomy group, mainly D and G trisomies. No effect of oral contraceptives was discovered. An increased frequency of chromosome anomalies occurred after ovulation-inducing therapy and after occupational exposure of the father to irradiation. No variations in the fertility rate and in the frequency of congenital malformations in births following abortions was noted. The incidence of recurring abortion was mainly influenced by the reproductive history of the couple before the karyotyped abortion.