The effectiveness of intrauterine insemination (IUI) combined with controlled ovarian hyperstimulation (COH) in the treatment of infertility with various etiologies was compared in a total of 152 cycles. Patients received a maximum of three IUI cycles for the treatment. Severe male (<2 x 10(6)motile sperm) or age facto. (> 39 y) patients were excluded in this study. Pregnancy was classified as clinical if a gestational sac was seen on ultrasound. The overall clinical pregnancy rate was 7.9% per cycle (12/152) and 9.7% per patient (12/124). The pregnancy rates were 0% in unstimulated natural (0/l8), 7.5% in CC (3/40), 8.2% in CC+hMG (4/49), 5.9% in GnRH-a ultrashort (1/17), 5.9% in GnRH-a long (1/17) and 27.3% in dual suppression cycles (3/11), respectively. The pregnancy rate was higher in dual suppression cycle than other stimulated cycles, but this was not significant. The multiple pregnancy rates were 25.0% (2 twins and 1 triplet). No patient developed ovarian hyperstimulation. Abortion rates were 66.7% in CC (2/3) and 100% in ultrashort cycles (1/1). The livebirth rate was 5.9% per cycle (9/152) and 7.3% per patient (9/124). There were no differences in age, duration of infertility, follicle size, total ampules of gonadotropins and days of stimulation between pregnant and non-pregnant groups. However, significant(P<0.05) differences were observed in the level of estradiol (E2) on the day of hCG injection (3,266.6+/-214.2 vs 2,202.7+/-139.4 pg/ml) and total motile sperm count (212.1+/-63.4 vs 105.1+/-9.9 x 10(6)) between pregnant group and non-pregnant group. These results suggest that lUl combined with successful ovarian stimulation tends to improve the chance of pregnancy as compared to lUl without COH and a total motile sperm count may be considered predictive of the success for pregnancy.