OBJECTIVE To examine the combined effects of factors influencing the pregnancy rates following controlled ovarian hyperstimulation (COH) and intrauterine insemination (IUI). STUDY DESIGN After utilizing the couple as the unit of analysis, 416 couples undergoing COH and IUI with the husband's sperm were studied retrospectively. RESULTS The woman's age, postwash total motile sperm counts and number of IUI treatment cycles were three major factors that affected the results of IUI. The predicted cumulative pregnancy rates under different values of the above three factors were therefore calculated using multiple logistic regression analysis and were compared to the pregnancy rate achieved by a cycle of in vitro fertilization and tubal embryo transfer. CONCLUSION Three treatment cycles of IUI are optimal for women aged < or = 34 with postwash total motile sperm counts > 5 x 10(6). For women either aged > or = 35 or with postwash total motile sperm counts < 5 x 10(6), the cumulative pregnancy rates achieved by IUI are extremely low, and other means of assisted reproduction are recommended for couples in those categories. However, this conclusion pertains to our clinics, and other institutions should establish their own data.