OBJECTIVE: To investigate the effects of somatostatin analogue, octreotide, given concurrently with recombinant human follicle stimulating hormone (rhFSH) on ovarian response to controlled ovarian stimulation (COS) according to body mass index (BMI) in infertile patients with polycystic ovary syndrome (PCOS) resistant to clomiphene citrate (CC). DESIGN: Prospective, randomized controlled trial. MATERIALS AND METHODS: COS was performed using GnRH antagonist multiple-dose protocol in early and late follicular phase (MDP-EL) for all patients. Patients were randomly allocated either to octreotide or control groups in each nonobese (BMI < 23)(n=80) and obese (BMI ≥ 23)(n=64) PCOS groups. For octreitide groups, 100 micrograms of octreotide were administered daily concomitantly with rhFSH from the starting day of COS up to the day of human chorionic gonadotropin (HCG) injection. RESULTS: Two cycles in the control group of nonobese patients and one cycle in the control group of obese patients were abandoned because of excessive follicular development. In nonobese patients, the number of follicles ≥ 14mm, serum estradiol and IGF-1 levels on the day of hCG injection, and the number of retrieved oocytes were lower in octreotide group (P<0.001, P<0.001, P=0.005, P=0.002, respectively). However, in obese patients, there were no differences in COS results except rhFSH dose used between octreotide and control groups. In nonobese patients, the incidence of severe ovarian hyperstimulation syndrome (OHSS) was lower in octreotide group, with 15% (6/40) compared with 0% in control group (P=0.026). There were no differences in the clinical pregnancy rate and miscarriage rate between octreotide and control groups in both nonobese and obese groups. CONCLUSION: Octreotide supplementation to rhFSH in COS cycles is beneficial in reducing the excessive follicular development and the incidence of severe OHSS without a deleterious effect on pregnancy outcome in nonobese PCOS patients, but this treatment does not work in obese PCOS patients.