BACKGROUND Polycystic ovary syndrome (PCOS) is among the most common endocrine disorders in premenopausal women, affecting 7-10% of this population. This syndrome is characterized by hyperandrogenism, chronic anovulation and, frequently, obesity. Hyperandrogenemia seems to be a consistent reproductive phenotype in male relatives as well as female relatives of PCOS women. This phenotype appears to have a genetic basis in PCOS families and shows significant linkage and association with a marker locus on chromosome 19p in the region of the insulin receptor (allele 8 of D19S884.). This allele is also recently found to be associated with a metabolic phenotype in PCOS probands and their brothers, including increased post-challenge glucose levels, apparent defects in insulin secretion, especially in response to sulfonylurea, and accelerated weight gain with age (unpublished date). Therefore, allele 8 status in PCOS probands and their family members can identify the reproductive and metabolic abnormalities.