Aims: To discuss some of theories regarding the origins of polycystic ovary syndrome (PCOS), the commonest hormone condition of women in the reproductive age. PCOS occurs in 5 10% of the population and has familial and environmental elements to its origin. The aim of this talk is to look at the aspects that suggest epigenetic modification of the familial factors that predispose to PCOS and also to discuss the environmental precipitants that may initiate PCOS in a susceptible individual. Study design: The literature will be systematically reviewed to look at those papers that cover genetic and epigenetic predisposing factors to PCOS. Subjects: Women with PCOS and their families as well as information derived from experimental animal studies. Outcome measures: The prevalence and severity of PCOS. Results: There is strong evidence that genetic factors may play a role in PCOS but in a recent paper Hickey et al were able to demonstrate epigenetic effects within families. Environmental factors such as obesity play a major role in the expression of the disease. Conclusions: There are clearly familial/genetic components to PCOS and environmental factors including diet, play a significant role in expression of the disease. Epigenetic factors are still debated but there is interesting information to suggest that this may play a role.