In 4 children, two boys aged 15 and two girls aged 17 years, thrombocytopenia was found with thrombocyte size of about the diameter of an erythrocyte, so called giant platelets. In 3 of the patients no signs of increased bleeding tendency were present, while the fourth had bruises, small stature and subnormal hearing. The 50-year-old father of 2 of the patients (a brother and sister) had thrombocytopenia with giant platelets as well. The patients without an increased bleeding tendency were advised to carry a 'medical alert.' Thrombocytopenia with giant platelets can be part of a hereditary syndrome in which other organ systems may be involved, e.g., kidneys, ears (hearing loss) or eyes (cataract). Morphological assessment of thrombocytes in children with chronic thrombocytopenia can contribute to the prevention of ineffective therapy (corticosteroids, gammaglobulin, splenectomy).