Objective: To compare efficiency of conventional and chronic low-dose regimens for treatment of anovulation associated with polycystic ovary syndrome (PCOS). Design: Fifty participants divided into two equal groups. The first group was treated with urinary human FSH using a conventional stepwise protocol and the second group was treated with a regimen of chronic low-dose and small incremental rises with urinary human FSH or with recombinant human FSH for a maximum of three cycles. Setting: Tertiary referral university hospital fertility unit. Patients: Fifty infertile women with clomiphene citrate-resistant anovulation associated with PCOS. Main Outcome Measures: Pattern of follicular development, amount of FSH required, serum E(2) concentrations, cycle fecundity, cumulative conception, and live birth rates, Multiple pregnancy and ovarian hyperstimulation syndrome (OHSS) rates. Results: Compared with the conventional dose protocol, the chronic low-dose regimen yielded slightly improved pregnancy rates (40% versus 24%) while completely avoiding OHSS and multiple pregnancies, which were prevalent (11% and 33%, respectively) with conventional therapy. Monofollicular development was induced in 74% versus 27% of cycles, and the total number of follicles > 16 mm and E(2) concentrations were half those observed on conventional therapy. Conclusions: For women with PCOS, a chronic low-dose regimen of FSH eliminated complications of OHSS and multiple pregnancies while maintaining a satisfactory pregnancy rate. This modality, thus, has distinct advantages and could well replace conventional gonadotropin therapy for these patients.