Essential thrombocythemia (ET) is a rare disorder in children. An 11-year-old white boy was first seen in January 1986 with symptoms of abdominal pain. His platelet count was 1.5 million/mm3. Other hematological values and coagulation studies, including bleeding time, were normal. There was laboratory evidence of mild platelet dysfunction. Using the criteria of the Polycythemia Vera Study Group, a diagnosis of ET was made. He developed frequent headaches. Aspirin was prescribed for the next 2 years at varying doses and frequency. During the period, platelet counts ranged between 1 and 3 million/mm3. In view of progressive headaches and evidence of increasing platelet dysfunction, further treatment was indicated. The use of a new agent, anagrelide, reported effective in adults with ET, resulted in amelioration of symptoms and improvement in quantitative and qualitative platelet control with no significant untoward effects.