Among 639 spontaneous abortions between the 8th and 14th week of gestation 342 (53.5%) revealed an abnormal karyotype. While the rate of trisomies distinctly increased with advancing maternal age, a decrease in the rate of 45,X conceptuses and polyploidies was observed among abortions from older women. The overall relation of XXXX:XXYY among the tetraploidies was 14:11 and that of XXX:XXY:XYY among the triploidies was 26:36:1. However, when the latter was related to maternal age, a reversal of the XXX:XXY ratio of 1:2 in the younger to 2:1 in the older age groups became evident. Furthermore a decrease in the rate of "paternally" derived partial hydatidiform moles was found among the triploid abortion specimens from older women. From these observations we conclude that digyny plays a major role in the origin of triploidy in the increased maternal age groups, while diandry related to immaturity of oocytes and impairment of oocyte cortical function is more frequent in triploid abortions from younger women.