The objective of this study is to evaluate the performance of clomiphene citrate (CC) challenge test to predict diminished ovarian reserve before controlled ovarian hyperstimulation for intracytoplasmic sperm injection (ICSI). The 198 women who underwent the CC challenge test fulfilled the following criteria; over 35 years of age, removal of one ovary or previous ovarian surgery, the presence of ovarian endometrioma or previous poor response to ovarian hyperstimulation. Of the patients tested, 141 were found to have a normal CC challenge test while 57 had an abnormal result. The cancellation rate of the cycle with a poor response was significantly higher in women with an abnormal test (36.8%) than in those with a normal test (19.8%) (P < 0.05). The sensitivity of CC test for cycle... cancellation was found to be 43% with a specificity of 76%, positive and negative predictive values of 37 and 80%, respectively. The estradiol values on hCG day, the number of retrieved oocytes and metaphase II oocytes and the rate of transfer cycles were significantly lower in females with an abnormal test. Women with normal test results had higher pregnancy rates per embryo transfer than those with abnormal test results (21.5 vs. 13.3%) and the predictive value of an abnormal test for failing to conceive was 93% (53/57) with a sensitivity of 31%, specificity of 84% and negative predictive value of 15.6%. Of 57 women with an abnormal test result, 25 (43.8%) were abnormal due only to an elevated day 10 or 11 value of FSH, which could not be detected using only basal FSH screening. In this group, the cancellation rate (48 vs. 19.8%, P < 0.01), the rate of transfer cycles (48 vs. 72.3%, P < 0.05) and the mean number of retrieved oocytes (4.9 +/- 2.5 vs. 6.4 +/- 3.1, P < 0.01) were all significantly different from normal test group. Although the rate of pregnancies per started cycle (8 vs. 15.6%) did not show a statistically significant difference, this is most probably due to the low number of patients. In conclusion, an abnormal CC challenge test is a good predictor of diminished ovarian reserve and it is better than a basal FSH concentration on day 3. It provides valuable information for both patients as to their chances of achieving a pregnancy and also for the medical team deciding on options for stimulation protocols.