Byline: Deborah E. McFadden (1), J. Tapio Pantzar (1), Gareth P. Jevon (1) Keywords: Key words: dysgenetic gonads, triploidy, sex differentiation Abstract: There are numerous reports describing the pathology of the fetus and placenta in triploidy. Although gonadal pathology is described in many of these reports, consistent changes have not been noted nor is it clear whether genital ambiguity can be considered part of the triploid phenotype. We present a case of triploidy of probable diandric origin, in which there were dysgenetic gonads with abnormal seminiferous tubules, nodules of undifferentiated stroma, and focal absence of the tunica albuginea. As this finding was distinctly unusual in our experience of triploid gonadal pathology, we reviewed the gonadal histology in 51 fetal and infant triploids examined in our autopsy/embryopathology laboratory. The gonads were compared to age-matched normal controls to determine if there was a specific gonadal pathology associated with triploidy and if there was any correlation of this pathology with parental origin of the triploidy. Our review of the triploid gonads indicated that while minor, nonspecific changes were not uncommon, overtly dysgenetic gonads, as observed in the index case, are rare. Author Affiliation: (1) Department of Pathology, Children's and Women's Health Centre of British Columbia and University of British Columbia, 4480 Oak Street, Vancouver, British Columbia, Canada V6H 3V4, CA Article note: Received June 2, 1999 accepted November 5, 1999.