Platelet activation is a link in the pathophysiology of diseases prone to thrombosis and inflammation. Numerous platelet markers, including mean platelet volume (MPV), have been investigated in connection with both thrombosis and inflammation. This review considers MPV as a prognostic and therapeutic marker as well as the factors influencing its measurement. Established cardiovascular risk factors, such as smoking, hypertension, dyslipidemia, and diabetes, can influence MPV, depending on confounding factors. Low-grade inflammation is one such factor. Evidence, particularly derived from prospective studies and a meta-analysis, suggest a correlation between an increase in MPV and the risk of thrombosis. High MPV associates with a variety of established risk factors, cardio- and cerebrovascular disorders, and low-grade inflammatory conditions prone to arterial and venous thromboses. High-grade inflammatory diseases, such as active rheumatoid arthritis or attacks of familial Mediterranean fever, present with low levels of MPV, which reverse in the course of anti-inflammatory therapy. Lifestyle modification, antihypertensive, lipid lowering and diet therapies can also affect MPV values, but these effects need to be investigated in large prospective studies with thrombotic endpoints.