Mean platelet volume (MPV), a parameter of complete blood count analysis, measures the average size of platelets. The alterations of MPV levels have been described as a diagnostic or prognostic predictor in patients with infectious diseases including sepsis, infective endocarditis, pneumonia, brucellosis, cellulitis, acute pyelonephritis, ascites fluid infection, hepatitis B or hepatitis C in recent studies. Although some matters still remain unclear, it can be said that MPV, especially in a scoring system, may be a cost-effective and useful marker for monitoring and predicting outcomes in patients with some infectious diseases in the future.