B AC K G R O U N D Metab olic syndrome (MS) has been assoc i ated with an inc r e ased risk of card io v a sc ular dis e ase and mort ality. Mean plat elet vol ume (MPV), an index of plat elet act iv at io n , has been shown to be inc r e ased in card iovascular and cerebrovascular dis e ase such as acute myoc a rd ial inf a r ct io n and acute isch emic stroke. The aim of this study was to i nv e st ig ate the rel at ion of MPV levels and MS. M ET H O D S A total of 868 adult individuals (mean age of 45.4±17.2) w ere enr o lled in the study. Subjects were grouped as MS (n= 461) and controls (n=407) acc o rding to the ATP III crit er ia. Four hundred sixty one subjects (53.1%) had t h r ee or more met ab olic fea t ures (38% in men and 62% in women). Two hundred thirty five subjects (27%) had high fasting gluc ose, 386 (44.5%) had elev ated bloo d pressure, 452 (52.1%) had high serum TG, 485 ( 55.9%) had low HDL chol e st erol, and 517 (59.6%) were obese. MPV levels were mea s ured along with the body mass index (BMI), blood press ure, lipids, gluc ose, plat elet mass and plat elet count levels. R E S U LT S MPV, platelet mass and plat elet counts did not differ acc o rding to metab olic comp onent counts. In add it ion, no c o rr el at ion was found betw een MPV and BMI, bloo d pressure, lipids, gluc ose, plat elet mass and plat elet cou n t levels. CO N C L U S I O N S In conclusion, this study with a considerably large population suggests that, though individual components of the disease seem to be associated with an increase in platelet size, MPV may not be an indicator of enhanced thrombotic activity in people with MS.