Objectives: to investigate whether body mass index (BMI), hypertension (HTN), diabetes, age, and physical activity can be considered risk factors for endometrial simple hyperplasia in premenopausal women. Furthermore this study was undertaken to determine whether serum concentration of leptin in patients with BMI ≥ 30 kg / m2 with endometrial hyperplasia deviate from values in patients with normal endometrium. Materials and Methods: The authors enrolled 167 hyperplasia cases and 282 controls. Demographic characteristics and data on age, diabetes, hypertension, BMI, physical activity, and anthropometric parameters were collected. Leptin concentration in serum was measured with immunoenzymatic test kit from IBL. Univariable and multivariable analysis were performed to verify the association among age, HTN, BMI, physical activity, diabetes, and the presence of uterine hyperplasia. Furthermore the authors evaluated the correlation between BMI and leptin level (with Pearson’s linear correlation) in women with simple hyperplasia and in controls. Results: The prevalence of hyperplasia found was 34.4%. The following factors were independently associated with increased risk of endometrial hyperplasia: HTN (odds ratio 3.19, 95% confidence interval 1.20 - 8.48, p < 0.020) and BMI ≥ 30 Kg / m2 (odds ratio 6.43, 95% confidence interval 3.92 - 10.53, p < 0.000). Mean leptin concentration in serum was higher in patients who had endometrial hyperplasia than in controls (p < 0.005) and the leptin levels depended on BMI. Conclusions: The following are risk factors for endometrial hyperplasia in premenopausal women: BMI ≥ 30 kg / m2 and HTN (blood pressure ≥ 130 / 85 or in therapy). Leptin appears to participate in proliferative processes of the endometrium, depending on BMI. Current guidelines may need to be reconsidered.