BACKGROUND Some studies propose that changes in leptin concentrations (above or under the normal range) result in infertility. Therefore, we investigated serum and follicular fluid leptin concentrations in infertile women with polycystic ovary syndrome (PCOS). OBJECTIVE To study serum and follicular fluid leptin concentrations in infertile women with PCOS. METHODS We conducted a case-control study. The case group consisted of 30 infertile women with PCOS who were admitted to the Infertility Department of Imam Khomainy Hospital in Ahvaz, Iran. The control group consisted of 30 healthy fertile women adjusted for age and body mass index (BMI) with the case group. On day 14 of the menstrual cycle, 5 ml of blood was obtained from subjects in both groups. Serum and follicular fluid leptin concentrations were determined by the enzyme linked immunosorbent assay (ELISA). A Biovendor kit was used for the measurement of leptin concentrations. All data were analyzed using statistical package for the social sciences (SPSS) software (version 17.0, Nie, Bent & Hull, USA). RESULTS There was a significant correlation between BMI and serum leptin concentrations in both the control (p=0.005, r=0.516) and case groups (p=0.006, r=0.547). In the case group, serum leptin concentrations were consistent with follicular fluid leptin concentrations (p<0.001, r=0.839). Comparison of serum leptin concentrations between the case and control groups revealed no significant difference (p=0.56). CONCLUSIONS Infertility among women with PCOS was not a consequence of changes in leptin concentrations.