Androgen excess is one of the most common reproductive endocrinologic abnormalities of women. Excluding specific etiologies such as androgen-secreting neoplasms and non-classic adrenal hyperplasia, the majority of androgen excess is functional in nature. It is clear that studies concerned with the heritability of this disorder greatly depend on how it is defined. Patients with the PolyCystic Ovary Syndrome (PCOS) are clearly included. However, we argue that ovulatory women with hirsutism and hyperandrogenemia should also be considered as affected which, together with PCOS, comprise the population of women we define as having Functional Androgen Excess (FAE). Our data, and that of others, suggests that FAE/PCOS is a familial disorder, with a single autosomal dominant gene effect and a variable phenotype. Inheritance appears to be equally probable from the maternal as from the paternal side of the family. Nonetheless, our data also suggests that the affection rate among mothers is less than expected, which may be due to decreased fertility of affected mothers, or to our inability to detect the disorder in older, menopausal or hormonally treated individuals. Finally, it appears that a woman's risk for developing PCOS is approximately 40% if her sister is affected. While considering FAE/PCOS to be a dominant genetic disorder with a high degree of expressivity, its highly variable phenotype suggests that besides a single genetic mutation other factors must be contributing to the development and expression of the disorder. These factors may include environmental influences (such as fat and carbohydrate consumption) exercise level, peripubertal stress and/or hormonal exposure; and additional genetic defects, such as those that regulate insulin secretion or determine body type.