Objectives: In patients with primary hyperparathyroidism (PHP), morbidity and mortality due to cardiovascular disease are seen more frequently than the normal population. Platelets play a significant role on the onset and progression of clotting and therefore contribute to the atherosclerotic process. Increased mean platelet volume (MPV) is an indicator of platelet activation. Therefore, it was defined as an independent risk factor for atherosclerotic process. The aim of this study was to compare MPV in patients with PHP and control subjects and also to assess postoperative MPV levels at third months. Materials and methods: We retrospectively reviewed the data of 74 patients with PHP and 71 controls matched for age, gender and presence of diabetes. Results: Age, gender and presence of diabetes were similar between the groups. (P=0.052, P=0.056 and P=0.374 respectively). MPV was found to be higher in patients with PHP compared to controls (8.64 +/- 1.20 fL and 7.77 +/- 0.88 fL, respectively) (P=0.01). There was no significant difference between the groups in terms of MPV levels both at the time of diagnosis and third month after surgery (P=0.136). Conclusions: In this study, we found MPV to be higher in patients with PHP than the controls as independent of diabetes. Also, this increase in MPV had been continued until the early stage of postoperative period.