The polycystic ovary syndrome (PCOS) is a complex polygenic disorder in which environmental factors play an important modifying role. We aimed to find differences in diet and life-style that might contribute to the development of PCOS among overweight or obese premenopausal women. We compared diet composition and self-reported physical activity among 22 patients with PCOS and 59 women without androgen excess recruited from a total of 113 consecutive premenopausal women reporting for management of weight excess. After correcting for a difference in age between women with PCOS and controls, there were no overall statistical significant differences between them in the total caloric intake, in the intake of macro- and micro-nutrients, caffeine, fiber and alcohol, in the proportion of women exercising regularly, or in the number of hours of exercise per week. The proportion of fat in the diets of the overweight and obese women irrespective of PCOS was well-above current recommendations, yet this excessive fat intake occurred at the expense of monounsaturated fatty acids mostly. In conclusion, diet composition and physical activity were apparently not decisive for the development of PCOS among overweight and obese premenopausal women.