PURPOSE:This study was undertaken to investigate the prevalence and the risk factors of thrombocytopenia in children taking valproate for convulsive disorders. METHODS:From Jan. 2000 to Dec. 2005, we reviewed the medical recordes of 54 children with convulsive disorders taking valproate over a period of 12 months. Then, we estimated the prevalence of thrombocytopenia, and analyzed the relationship between changes in platelet counts and other factors such as age, sex, serum valproate levels and the duration of valproate therapy. RESULTS:Six(11.1%) children taking valproate had at least one episode of thrombocytopenia. The platelet counts were significantly lowered at 3 months after valproate therapy and recovered after 6 months(P<0.05). The relationship between the platelet counts and other factors such as blood valproate levels, sex and age was not observed in our study. CONCLUSION:Thrombocytopenia can appear after a few months of therapy and regular monitorings of platelet counts in children taking valproate may be needed to prevent potential bleeding diathesis.