Background The main determinants of the level of leptin in human plasma are the fat mass and sex. In recent literature many papers have been published indicating the participation of leptin in the pathogenesis of essential hypertension. The aim of this study was to compare serum levels of leptin and evaluate its importance in the pathophysiology of hypertension in obese men and women. Material and methods The study was conducted in a group of a total of 52 obese individuals (26 women and 26 men) with newly diagnosed essential hypertension. The study protocol included blood sample collection for the measurements of biochemical parameters and hormone levels. Biochemical assays were performed using routine methods. Serum insulin was determined by immunoradiometric assay (IRMA). The index of insulin resistance (IR) was calculated using HOMA. Leptin, plasma renin activity (PRA) and plasma aldosterone concentration were determined by radioimmunoassay (RIA). Results No significant differences were found between women and men in terms of age, BMI, blood pressure, total cholesterol, LDL and fasting glucose. Men had slightly but significantly higher waist circumference. The group of women had significantly higher levels of leptin, insulin and insulin resistance, and a higher PRA and aldosterone levels than males. In the group studied, leptin significantly positively correlated with blood pressure, as well as with the concentration of aldosterone and renin both in women and in men. There was no similar relationship between leptin and insulin and the insulin resistance index. Conclusions Women with obesity and hypertension have higher levels of leptin than obese men with hypertension. Reported correlations between plasma leptin concentration and blood pressure suggest that it is directly or indirectly involved in the pathophysiology of hypertension in obese individuals regardless of gender.