Prior studies have demonstrated that gonadotropin stimulation quality and pregnancy rates are better in in vitro fertilization (IVF) patients with low basal cycle day 3 follicle-stimulating hormone (FSH) levels. The records of 81 patients who had undergone three or more IVF attempts during a 2-year period were studied to determine the degree and potential impact of intercycle variability in basal FSH concentrations. The mean of the individual standard deviations for all 81 patients was 4.2 +/- 0.4 mIU/mL. However, the patients with a mean basal FSH of less than 15 mIU/mL had a mean deviation of only 2.6 +/- 0.2 mIU/mL, whereas those with a mean basal FSH of greater than or equal to 15 mIU/mL had a mean deviation of 7.3 +/- 0.7 mIU/mL. Intercycle variability in basal FSH values did not predict changes in ovarian response to gonadotropin stimulation and thus may not be used to select an optimal cycle in which to stimulate an individual patient. Furthermore, patients with large intercycle variation responded poorly to gonadotropin stimulation independent of their basal FSH concentration. This information allows more precise counseling of patients regarding their appropriateness for assisted reproduction.