Context: Although it is well-established that adiposity increases the severity of the clinical features of PCOS, the data regarding the prevalence of PCOS in obese women and the change in body weight women presented with PCOS over time is scarce.

Objective: To determine whether: (1) obesity increases the risk of PCOS, and (2) the degree of obesity of PCOS patients has increased, paralleling the rise in obesity in the population.

Design: Analysis of data from two consecutive populational studies assessing the prevalence of PCOS and a database containing all untreated PCOS patients evaluated at a university clinic between 1987–2002.

Setting: Tertiary-care center.

Patients or Other Participants: 675 women who participated in prevalence studies and 746 PCOS patients.

Main Outcome Measures: Populational prevalence of PCOS according to body mass index (BMI), and change in BMI of PCOS patients over time.

Results: The prevalences of PCOS in underweight, normal weight, overweight, and obese women were 8.2, 9.8, 9.9, and 9.0%, respectively. Prevalence rates reached 12.4 and 11.5% in women with BMI 35–40 kg/m² and >40 kg/m² (NS). The mean BMI of PCOS patients diagnosed between 1987–2002 rose beginning in 1997 and reaching 37.3 ± 9.9 kg/m² in 2000–2002, paralleling the change in BMI of the surrounding population (10–14% obesity rate in 1987, 15–19% in 1997, and 25% in 2002).

Conclusion: Our results suggest that the risk of PCOS is only minimally increased with obesity, although the degree of obesity of PCOS patients has increased, similar to that observed in the general population. These data indicate that obesity in PCOS reflects to a great extent environmental factors.