In the present study the phospholipid and fatty acid concentration of platelet has been measured in patients with poorly and well controlled diabetes mellitus and in control subjects. An increased phosphatidylethanolamine (p less than 0.01) and phosphatidylserine (p less than 0.001) content of platelets was found in poorly controlled diabetes as well as an increased phosphatidylserine (p less then 0.001) concentration in well controlled diabetes. The most notable changes of platelet fatty acids were a decreased concentration of palmitic (16:0; p less than 0.01) and linoleic acid (18:2; p less than 0.001) in the poorly controlled diabetes as well as (p less than 0.001) and (p less than 0.025) in the well controlled diabetes, respectively. Also, an increased concentration of arachidonic acid (20:4; p less than 0.001) was found in both groups of diabetics. No differences were found in phospholipid concentration between patients with and without vascular diseases.