Objectives. In our study we sought to determine whether mean platelet volume (MPV), measured on admission, could be used in determining decreased coronary blood flow (CBF) in stable coronary artery disease (CAD) patients after percutaneous coronary intervention (PCI). Background. Platelets play a crucial role in the pathophysiology of CAD. MPV reflects platelet function and activity. There are no reports regarding the effect of MPV on CBF in patients with stable CAD undergoing PCI. Methods. A total of 66 consecutive patients (mean age: 58 +/- 5 years, 74% male) with the diagnosis of stable CAD who were hospitalized for PCI were prospectively enrolled in our study. Coronary flow rates of all subjects were documented by corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC) for each major coronary artery before and after PCI. Blood samples for MPV estimation, platelet count and other laboratory data obtained on admission were measured on the day of the scheduled PCI. Patients were divided into two groups according to MPV levels measured on admission: 1) high MPV group and 2) normal MPV group. Results. A final TIMI 3 flow was achieved in all patients with no complications. Procedural characteristics of PCI, except left anterior descending artery intervention, were similar in the two groups. Patients with high MPV had significantly higher CTFC than those with a normal MPV (24 +/- 3 vs. 17 +/- 5; p = 0.001). The MPV correlated strongly with post-PCI CTFC (R = 0.625; p = 0.0001). Multiple logistic regression analysis showed that only MPV was an independent predictor of post-PCI CTFC after adjustment for baseline characteristics (OR 1.9, 95% CI 1.2-2.3; p = 0.001). Conclusions. MPV may be considered a useful hematological marker, allowing for early and easy identification of patients with stable CAD who are at a higher risk of post-PCI low-reflow.