['To determine the impact of the time interval from the end of sperm preparation (TSP) to intrauterine insemination (IUI) on the outcome.', 'Prospective multicentre cohort study.', 'Seven French centers (assisted reproduction group in northeastern France, four academic centers, and three clinics).', 'Eight hundred sixty-two IUI cycles (709 patients) managed by gonadotropins were studied.', 'Cycles were stimulated by either FSH or hMG, and hCG was administrated when the leading follicle diameter measured >15 mm. IUIs were performed ∼ 36 hours after ovulation triggering.', 'Generalized linear mixed models for binary outcomes were used to model clinical pregnancy (CP) to assess the effect of TSP adjusted for other predictors (such as maternal age, semen quality, and indication of IUI treatment).', 'The TSP effect was significant, featuring an inverse U-shaped curve admitting an optimum interval of ∼ 40-80 minutes improving CP compared with other values. Other significant predictors were total motile spermatozoa inseminated, maternal age, and unexplained infertility.'] Is clinical success of intrauterine insemination cycles affected by the sperm preparation time?