Polycystic ovary syndrome (PCOS) is characterized by clinical or biochemical hyperandrogenism, oligo-anovulation and polycystic ovarian morphology on ultrasound. Although the ovaries are the primary source of hyperandrogenism in PCOS, between 20% and 30% of patients with PCOS demonstrate adrenal androgen (AA) excess, as reflected by the circulating dehydroepiandrosterone sulfate (DHEAS) levels. The contribution of AA excess to the development or phenotypic expression of PCOS is not fully understood. Women with PCOS, particularly those with hyperandrogenic subphenotypes, show generalized hypersecretion of adrenocortical products, basally and in response to adrenocorticotropic hormone (ACTH). Alterations in adrenocortical biosynthesis, an exaggeration in the responsivity to ACTH, defects in cortisol metabolism and extra-adrenal factors, including obesity, insulin and glucose levels, and ovarian secretions play a limited role in increased AA production observed in PCOS. Adrenal androgen (AA) levels and their response to ACTH stimulation are highly individualized and relatively constant over time, suggesting that AA hypersecretion may be an inherited trait. Familial aggregation of AA excess in both brothers and sisters of patients with PCOS also supports heritability. However, studies to date have failed to identify specific genetic defects in adrenocortical dysfunction of PCOS due to the genetic and phenotypic heterogeneity of the syndrome and the lack of insufficiently large cohorts.