In the clinical management of in-vitro fertilization (IVF) patients it would be very useful to know, before the embryo transfer, whether or not there is a significant chance of pregnancy in that cycle. If low, it would be better to freeze the embryos and postpone the embryo transfer to a subsequent cycle. For this reason, a retrospective study was carried out to investigate the correlations between the serum CA-125 values before embryo transfer and the clinical outcome of that IVF cycle. Women aged <40 years undergoing a complete infertility evaluation including laparoscopy and receiving gonadotrophin-releasing hormone analogue (GnRHa) suppression followed by purified follicle stimulating hormone (FSH) for IVF-embryo transfer were entered into the study. Ninety-seven cycles qualified for evaluation (26 pregnant and 71 non-pregnant cycles). CA-125 concentrations on the day of oocyte retrieval were significantly lower in the pregnant versus non-pregnant cycles in both non-endometriosis and endometriosis patients. To evaluate the existence of a cut-off value of CA-125 which would allow the prediction of a possible pregnancy with sufficient specificity and sensitivity, a receiver operating characteristic curve analysis was performed. This analysis demonstrated the absence of any predictive value of the subsequent pregnancy for CA-125 concentrations. For this reason, and in contrast with previous findings, CA-125 determinations before the embryo transfer in IVF patients do not appear to be a useful tool for clinicians to use in predicting the outcome of IVF in any given cycle.