Thrombocytopenia is frequently observed in vivax malaria but the exact mechanism has not been elucidated. We studied 27 cases of acute vivax malaria out of which 24 cases had thrombocytopenia. This was the most common hematological finding. None had bleeding from any site. Anaemia and splenomegaly were not present in any of the cases. Platelet counts reverted to normal on treatment. Other causes of thrombocytopenia were ruled out by complete history and physical examination, dengue serology and blood culture. DIC was ruled out by peripheral smear examination and measurement of FDP levels. Our study stresses the importance of thrombocytopenia as an early indicator for acute malaria; a finding that is frequent and present even before anemia and splenomegaly set in. The possible mechanisms leading to thrombocytopenia in malaria have been discussed which include immune mechanisms, oxidative stress, alterations in splenic functions and a direct interaction between plasmodium and platelets.