Polycystic Ovary Syndrome (PCOS) is one of the most common endocrine disorders in women. Its marked phenotypic variability, puzzling list of associated conditions, and hence potential risk to a woman's health over her lifecycle clearly remain a clinical investigational, genetic, and therapeutic challenge. To a great extent, this variability can be attributed to the marked genetic and environmental heterogeneity of the populations studied. We plan to address many of these long-term clinical research obstacles by delineating the genetic basis of PCOS in a unique investigational venue, the Icelandic population. Studying the Icelandic population has the following advantages: a) the population's relative genetic and environmental homogeneity; b) the remarkably rich genealogic database; and c) the centralized healthcare information. In this unusual venue, clustering of large numbers of PCOS families with known relationships is possible. Their relative homogeneity and genealogic characteristics can reduce genetic variance and hence be used to map the genetic basis for PCOS more efficiently than in more heterogeneous populations. As the genes responsible for PCOS emerge, this protocol will also determine phenotype/genotype correlations in Iceland, contrasting them with US women, and assess their long-term medical consequences.