Familial aggregates of the most common disorders of mullerian differentiation in females-Mullerian aplasia, incomplete Mullerian fusion-are best explained on the basis of polygenic/multifactorial inheritance. No information exists on the number and chromosomal location of responsible genes. Single mutant genes (Mendelian) are responsible for the McKusick- Kaufman syndrome (MKS) and the hand-foot-genital syndrome. The molecular basis for the latter condition involves HOXA13, but the molecular basis of MKS and other disorders of the female reproductive ducts is unknown. Vaginal atresia, Mullerian aplasia, and incomplete Mullerian fusion are not infrequently observed in malformation syndromes. (C) 2000 Wiley-Liss, Inc.