Background Primary immune thrombocytopenia is a bleeding diathesis with an unknown etiology in predisposed individuals with immune disturbances. Although it is claimed that children and adults differ in clinical and laboratory aspects, few data exist to corroborate this observation. Our objective was to assess comparative data from children and adults with newly diagnosed immune thrombocytopenia. Design and Methods Clinical and laboratory data of 1,784 children and 340 adults were extracted from the Pediatric and Adult Registry on Chronic Immune Thrombocytopenia. The registry represents a prospective cohort of children and adults with newly diagnosed immune thrombocytopenia. Participating investigators registered their patients immediately after the diagnosis using a web based data transfer. Children aged under 16 years were compared with adults aged 16 years and over with descriptive statistical analyses. Results The presenting mean platelet count of children and adults was 18.1 and 25.4x10(9)/L. Signs of bleeding were reported in 24% of children and in 23% of adults, and intracranial hemorrhage in 10 of 1,784 children and in 6 of 340 adults. Co-morbidity was observed in 3.9% of children and in 30% of adults. Bone marrow aspiration and laboratory tests (antinuclear antibodies, human immunodeficiency and hepatitis C virus) were performed more frequently in adults. Children and adults were followed with a 'watch and wait' strategy in 20% and in 29%, respectively. Immunoglobulins were used more frequently in children and corticosteroids in adults. Conclusions Comparative data of children and adults with newly diagnosed immune thrombocytopenia revealed similarities in presenting platelet counts and in bleeding, whereas differences occurred in co-morbidity, diagnostic procedures and therapy.