This paper is based on a Cochrane review published in The Cochrane Library, issue 2, 2001 (see www.CochraneLibrary. net for information) with permission from The Cochrane Collaboration and Update Software. Cochrane reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and The Cochrane Library should be consulted for the most recent version of the review. This systematic review was performed to study the efficacy and safety of recombinant FSH (rFSH) versus urinary FSH (uFSH) and to compare different dose regimens of rFSH for ovulation induction in women with clomiphene-resistant polycystic ovary syndrome (PCOS). Six randomized controlled trials were included in the review, according to the principles of the Cochrane Menstrual Disorders and Subfertility Group. Three trials compared rFSH with uFSH and three trials compared two different treatment regimens of rFSH. Participants were women with clomiphene citrate-resistant PCOS. Main outcome measures were ovulation, clinical pregnancy, miscarriage, multiple pregnancy, ovarian stimulation syndrome (OSS), total gonadotrophin dose used and total duration of stimulation. Summary statistics were expressed as odds ratios. Data from the trials comparing rFSH and uFSH could be pooled. There was no evidence of a difference between rFSH and uFSH in any of the outcomes. Data from the trials comparing different dose regimens of rFSH could not be combined, and for each comparison there was insufficient evidence of a difference. More randomized clinical trials with sufficient power are necessary to estimate the difference, if one exists, between rFSH and uFSH and between different dose regimens of rFSH.