Secondary forms of immune thrombocytopenia (ITP) represent approximately 20% of all ITP cases in adulthood and this rate increases with age. Since some causes may influence both the prognosis and outcome but also the management of ITP, a minimal workup must be performed at ITP diagnosis to look for an associated or underlying cause. Among adults, B-cell lymphomas and mainly chronic lymphocytic leukemia, systemic auto-immune diseases such as systemic lupus or primary immunodeficiencies mainly represented by common variable immunodeficiency are the most frequent causes of secondary ITP. Whereas first-line therapy used for secondary ITP is usually similar to the one commonly used in primary ITP and relies mostly on corticosteroids±intravenous immunoglobulin according to the severity of bleeding, second and third-line treatments must take into account the type and degree of activity of the underlying disease.