Platelets activation processes comprise very complex signalling pathways which involve a G protein system, coupled to effect enzymes such as phospholipase A2, phospholipase C, guanilil and adenilil cyclases. Closely related functional properties and special estructural characteristics of platelets confer them a very high trombogenic potential, which play a role in the development of stroke, from the primary hemostasis. Basis of platelet aggregation, activation, degranulation and platelet participation in cerebrovascular disease were reviewed. Usage of antiplatelet agents, and novel anti-membrane-glycoproteins therapies were emphasized.