Purpose of investigation: To assess the accuracy of CA-125 determination associated with clinical history and of the neutrophil/lymphocyte (N/L) ratio for a presumptive diagnosis of endometriosis in women with chronic pelvic pain (CPP). Materials and Methods: This was a cross-sectional study of data from the medical records of women with CPP submitted to laparoscopy from August 1999 to January 2009 at the University Hospital. The performance of the evaluation of CA-125 and of the N/L ratio for the prediction of endometriosis was compared based on the corresponding ROC curves and their 95% confidence intervals. Results: CA-125 levels were significantly higher in women with CPP and endometriosis and their association with a complaint of dysmenorrhea improved their sensitivity. For a cut-off of 20 IU/ml, the predictive value for a diagnosis of endometriosis in women with CPP was 97.6%. Dyspareunia, subfertility, and N/L ratio were not useful for a diagnosis of endometriosis in women with CPP. Conclusion: The association of elevated CA-125 levels with a complaint of dysmenorrhea is adequate in a presumptive and accurate diagnosis of endometriosis in this specific group of women with CPP, permitting an early institution of clinical treatment without the need of previous laparoscopic confirmation.