Objective: To assess the diagnostic performance of serum CA-125 measurement in the detection of endometriosis. Design: Meta-analysis. Setting and Patient(s): Twenty-three studies comparing serum CA-125 levels and laparoscopically confirmed endometriosis. Intervention(s): Serum CA-125 measurement and laparoscopy. Main Outcome Measure(s): Sensitivity and specificity of serum CA-125 measurement in the diagnosis of endometriosis with laparoscopy as the reference standard. Result(s): The estimated summary receiver operating characteristic curves showed that the performance of serum CA-125 measurement in the diagnosis of endometriosis grade I/IV is limited, whereas its performance in the diagnosis of endometriosis grade HI/IV is better. Conclusion(s): Despite its limited diagnostic performance, we believe that the routine use of serum CA-125 measurement in patients with infertility might be justified. In contrast to laparoscopy, serum CA-125 measurement is an inexpensive test that is not a burden for the patient. It could identify a subgroup of patients who are more likely to benefit from early laparoscopy. Studies reporting on the mutual dependence between serum CA-125 measurement and data from the history and physical examination are needed.