BACKGROUND The artificial insemination is the introduction of spermatozoa in the feminine genital tract without carrying out sexual contact and with the purpose of obtaining the pregnancy. The insemination intrauterine has improved its rate of success thanks to the technological advances and the best knowledge of human reproductive physiology. OBJECTIVE To evaluate the prognostic factors for the pregnancy success and calculate the cumulative rate per cycle in IUI (intrauterine insemination). METHODS This study was descriptive, retrospective, analytic, and longitudinal. The cycles of IUI were analyzed from January 1st 2003 to December 31st 2005. Couples 24-41 years old with primary and secondary infertility were included. The following variables were studied: age of participant, type of infertility, length of infertility, aetiology, postcapacitation sperm density and motility, number of follicles, endometrial thickness, and the cycle number in which the IUI was performed. Patients carried out a protocol of ovarian stimulation and follicular follow up. The results were analyzed with 11.0 SPSS, continuous variables were analyzed and reported as means +/- SD with univariate logistic regression to determine statistic significance. Categoric variables were reported in frequencies and percentages. ROC curves were calculated to determine optimal cutting points. RESULTS 668 cycles were analyzed in 391 couples. The pregnancy rate per cycle and couple was of 13.0 and 21.7% respectively. Means +/- SD patient age was 33.5 +/- 3.4 years old. The three variables with p < 0.05 were: the infertility duration, sperm motility and the cycle number in which IUI was performed. No statistical significance was found in the remaining variables. CONCLUSIONS The greatest success in IUI will be achieved with infertility of 4 years or less, with sperm motility of 77.6% and in the first two cycles of treatment.