A prospective, population-based registration of children with immune thrombocytopenic purpura (ITP) was performed in Norway in 1996 and 1997. Ninety-two cases were identified, indicating an incidence of 5.3 per 100,000 children under 15 years. The sex ratio (female/male) was 1.2/1. Fifty-six percent presented with cutaneous signs only. The lowest platelet count was < 20 x 10(9)/L in 91%. In spite of mild bleeding symptoms, medical treatment was given in 68%, in most cases (57/63) with intravenous immunoglobulin. A total of 41/44 patients with platelet counts of < or = 5 x 10(9)/L were treated, regardless of whether they had mucous bleedings or not. Eighteen percent had platelet counts < 150 x 10(9)/L at 6 months, and 9% at 12 months following diagnosis. One patient with therapy-resistant chronic ITP died 16 months after diagnosis from an anesthesia complication related to profound epistaxis. This study shows a relatively high incidence. As in other studies, there was a tendency to treat platelet counts rather than bleeding symptoms.