OBJECTIVE: To evaluate basal metabolic rate (BMR) in women with PCOS and to determine its association with insulin resistance (IR).DESIGN: Prospective assessment of BMR in women with PCOS.SETTING: Outpatient clinic of the Division of Reproductive Endocrinology.PATIENT(S): The study included 91 Greek women with PCOS and biochemical hyperandrogenemia, with mean age 24.03 +/- 0.55 years and mean body mass index (BMI) 26.67 +/- 0.69 kg/m(2), and 48 matched regularly menstruating women, with mean age 26.33 +/- 0.93 years and mean BMI 23.35 +/- 0.85 kg/m(2), as control subjects.INTERVENTION(S): Assessment of BMR by indirect calorimetry, IR by HOMA and QUICKI indices, fasting insulin, and fasting glucose/insulin ratio.MAIN OUTCOME MEASURE(S): Reduced BMR in PCOS with or without IR.RESULT(S): Adjusted BMR was 1,868 +/- 41 kcal/day in the control group, 1,445.57 +/- 76 in all PCOS women, 1,590 +/- 130 in PCOS women without IR and 1,116 +/- 106 in PCOS women with IR. Adjusted BMR showed a statistically significant difference between women with PCOS and control subjects, with lowest values in the group of PCOS women with IR, even after adjusting all groups for age and BMI.CONCLUSION(S): Women with PCOS, particularly those with IR, present a significantly decreased BMR.