The candidate gene approach has already paid some dividends in trying to understand the complex genetics of polycystic ovary syndrome (PCOS). In terms of steroidogenic abnormalities, CYP11a-encoding P450 side chain cleavage-appears to be a major susceptibility locus. In relation to the well-described metabolic disturbances in PCOS, the insulin gene variable number tandem repeat (VNTR) appears to be a promising candidate, at least in populations studied in the UK. Finally, genes implicated in ovarian follicular development may have a role in the aetiology of PCOS, as demonstrated by recent identification of the follistatin gene as a potential disease locus. It seems unlikely that PCOS can be explained on the basis of a single gene disorder although, in a given family, one gene may have a predominant effect. An oligogenic model seems the most appropriate basis on which to understand the genetic origins of this very common disorder. The candidate gene approach has been useful to date, but it may prove important in the near future to perform an anonymous genome-wide scan to identify hitherto unheralded susceptibility loci.