BACKGROUND Intra-uterine insemination (IUI) is one of the most frequently used fertility treatments for couples with male subfertility. Its use, especially when combined with ovarian hyperstimulation (OH) has been subject of discussion. Although the treatment itself is less invasive and expensive than others, its efficacy has not been proven. Furthermore, the adverse effects of OH such as ovarian hyperstimulation syndrome (OHSS ) and multiple pregnancy are a concern. OBJECTIVE The aim of this review is to determine whether for couples with male subfertility, IUI improves the live birth rates or ongoing pregnancy rates compared with timed intercourse (TI), with or without OH. METHODS We searched the Cochrane Menstrual and Disorders Subfertility Group Trials Special Register, the Cochrane Central Register of Controlled Trials (the Cochrane Library, 2006, issue 3), MEDLINE (1966 to May 2006), EMBASE (1980 to May 2006), SCIsearch and the reference lists of articles. We hand searched abstracts of the American Society for Reproductive Medicine, the European Society for Human Reproduction and Embryology. Authors of identified articles were contacted for unpublished data. METHODS Randomised controlled trials (RCT's) with at least one of the following comparisons were included: 1) IUI versus TI or expectant management both in natural cycles 2) IUI versus TI both in cycles with OH 3) IUI in natural cycles versus TI + OH 4) IUI + OH versus TI in natural cycles 5) IUI in natural cycles versus IUI + OH Couples with abnormal sperm parameters only were included. METHODS Two co-reviewers independently performed quality assessment and data extraction. Where possible data were pooled, and a meta-analysis was performed. Sensitivity and subgroup analyses were carried out where possible and appropriate. RESULTS Three trials of parallel design, and five trials of cross-over design with pre-cross-over data were included in the meta-analysis. Three compared IUI with TI both in stimulated cycles. The remaining four of these studies compared IUI versus IUI + OH . Three studies reported on our main outcome of interest live birth rate per couple. For the comparison IUI versus TI both in natural cycles no evidence of difference between the probabilities of pregnancy rates per woman after IUI compared with TI was found (Peto OR 5.3, 95% CI 0.42 to 67). No statistically significant of difference between pregnancy rates (PR) per couple for IUI + OH versus IUI could be found (Peto OR 1.47, 95% CI 0.92 to 2.37). For the comparison IUI versus TI both in stimulated cycles there was no evidence of statistically significant difference in pregnancy rates per couple either (Peto OR 1.67, 95% CI 0.83 to 3.37). There were insufficient data available for adverse outcomes such as OHSS, multiple pregnancy, miscarriage rate and ectopic pregnancy to perform a statistical analysis. For the other two comparisons no RCT's were found which reported pregnancy rates per couple. A further 10 studies which included one of the comparisons of interests were found. Since these studies reported pregnancy rates per cycle only these data could not be included in the meta-analysis. CONCLUSIONS There was insufficient evidence of effectiveness to recommend or advise against IUI with or without OH above TI, or vice versa. Large, high quality randomised controlled trials, comparing IUI with or without OH with pregnancy rate per couple as the main outcome of interest are lacking. There is a need for such trials since firm conclusions cannot be drawn yet.