In view of the rare presence of studies concerning platelet function as risk factor in atherosclerotic patients, processes underlying thromboembolic events are reviewed in this paper. The morphology and the structural organization-membrane receptors, the open canalicular and dense tubular systems, the cytoskeleton, mitochondria, granules, lysosomes, and peroxisomes-of platelets are described. Platelet function under physiological conditions in atherosclerosis and after implantation of cardiovascular devices is summarized.