The finding of a prolonged bleeding time in a patient whose platelet count is normal suggests some abnormality in the function of the platelets. This situation may be due to an inherent platelet defect or to the deficiency of a plasma factor necessary for some aspect of platelet function. Defects of platelet function are also seen in a wide range of disease states and may be caused by many different classes of drugs. Simple methods are available to identify abnormalities in platelet numbers and/or function. Tests of platelet aggregation, using the aggregometer, are now widely used to investigate patients suspected of having platelet disorders. We observed in the last four years that thrombocythopenia is quite common amongst children and bleeding from platelet dysfunction, congenital or acquired, is not rare in Malaysia. This study was done to assess the prevalence of platelet abnormality in a section of the general 'healthy' population of school-going children and to study the possible causes of any abnormalities detected.