Immune thrombocytopenic purpura (ITP) is divided in an acute and chronic form based on the duration of the disease. Persistence of thrombocytopenia for more than 6 months defines chronic ITP. The disease occurs in both children and adults with acute ITP as the predominant form of childhood and chronic ITP occurring in approximately 20% of children and almost all adult patients. The diagnostic procedures and the therapeutic consequences are discussed with respect to the many open and unresolved questions recently identified by a panel of pediatric and adult hematologists on behalf of The American Society of Hematology. Research activities with identification of priorities are important to better understand the disease resulting in an optimal evidence-based management of children and adults with ITP.