Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism and increases the risk of premature cardiovascular diseases. In patients with FH, platelet function may be activated; however, the extent of this activation and its etiology are unclear. We aimed to evaluate the mean platelet volume (MPV), a marker of platelet activation, in patients with FH. The study group consisted of 164 patients with FH and 160 control patients. Controls were matched for age, gender, hypertension, and smoking. The MPV was significantly higher in patients with FH than in controls (9.2 +/- 0.4 vs 7.9 +/- 0.6 fL, respectively; P < .001). Platelet count was significantly lower among patients with FH when compared to control patients (259 +/- 51 vs 272 +/- 56 x 10(3)/L, respectively; P = .03). In linear regression analysis, MPV was independently associated only with total cholesterol ( = .6, 95% confidence interval: 0.004-0.008, P < .001). We have shown that MPV was increased in patients with FH and that it was independently associated with total cholesterol level.