Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders among women at reproductive age. Its classical form is characterized by menstrual irregularities, chronic anovulation, infertility, and hyperandrogenism. The prevalence of obesity is high among women with POS and its causes have not been fully clarified. Hypotheses have been raised suggesting the possible presence of both abnormal energy expenditure and a reduced response of the gastrointestinal hormones responsible for the control of food ingestión, especially ghrelin. The specific effects of diet composition on POS have been little explored. It has been suggested that po-lyunsaturated fatty acids may improve insulin sensitivity and that high-protein diets may potentiate weight loss and improve reproductive function. However, current evidence is insufficient to determine the optimum composition of a diet for POS patients. The dietary conduct should focus on weight loss to be achieved with nutritionally complete and balanced diets.