Objective: Increased platelet activation has also been suggested to play a pivotal role in the development and progression of inflammation. Recently, mean platelet volume (MPV) has been investigated as a simple inflammatory marker in several diseases and it was found that MPV can be used as a marker of inflammatory disease. Therefore this study was designed to investigate and compare the values of MPV in patients with endometriosis and the MPV values in healthy women. Materials and methods: Patients with endometriosis (n = 297) and symptom-free, healthy, age-matched controls underwent tubal ligation (n = 36) were retrospectively evaluated and recruited to the study at three tertiary centers between January 2008 and December 2014. For further analysis, patients with endometriosis were divided into initial endometriosis (n = 129) and advanced endometriosis (n = 168) groups according to the severity of the disease. Receiver Operating Characteristic (ROC) curve and sensitivity and specificity report were performed for MPV value to evaluate differences between the groups. Results: MPV in patients with endometriosis were found to be higher than the control group (8.80 +/- 1.08 fL vs 8.11 +/- 1.03 fL, respectively; P < 0.001). There was no significant difference regarding mean MPV between the patients with advanced and initial endometriosis (8.72 +/- 1.60 fL and 8.90 +/- 0.97 fL, respectively; P = 0.15). ROC curve analysis suggested that the optimum MPV cut-off value for endometriosis was 8.55 fL, with a sensitivity, specificity, of 61% and 61%, respectively (AUC: 0.671). Conclusion: This study showed that significantly higher MPV levels were found in the patients with endometriosis and confirmed the previous studies indicating that endometriosis is an inflammatory process. MPV is an important, simple, inexpensive, and effortless hematological parameter and can be useful in evaluation of endometriosis patients.