Key Points• Incidence of ITP was 2.9/100 000 person-years with age, seasonal, and regional variations; in adults, 18% were secondary. • Severe (gastrointestinal or central nervous system) bleeding at ITP onset was rare (,1%); the risk increased with age.The epidemiology of immune thrombocytopenia (ITP) is not well known. The purpose of this study was to assess ITP incidence at a nationwide level (France) with recent data (mid-2009 to mid-2011; 129 248 543 person-years). The data source is the French health insurance database. We selected cases with diagnosis codes for in-hospital stays and long-term disease attributions, thus restricting our search to ITPs necessitating health care. We studied incidence by age, gender, calendar month, regions, and proportion of secondary ITPs, of ITPs becoming persistent or chronic, and of severe bleeding at disease onset. We identified 3771 incident ITP patients. Incidence was 2.9/100 000 person-years, with peaks among children and in those >60 years of age. ITP was more frequent among males in these subgroups. The incidence was lower in overseas Caribbean French departments, suggesting a lower incidence among Afro-American people. There was a northsouth gradient in mainland France and seasonal variations (peak in winter and nadir in summer). Persistence or chronicity occurred in 36% of children compared with 67% of adults. Among adults, 18% of ITPs were secondary. Malignancy was the main cause (10.9%). Myelodysplastic syndromes were not rare (2.3%). Severe gastrointestinal or central nervous system bleeding at ITP onset was rare (<1%). (Blood. 2014;124(22):3308-3315)

French health insurance databases are organized since 2003 into a huge digital data warehouse, the Système national d'information inter-régime de l'assurance maladie (SNIIR-AM). It covers the entire French population (65 million inhabitants). In order to facilitate studies on more frequent conditions, a random sample of 1/97th of national health system beneficiaries has been built since 2005, called the échantillon généraliste des bénéficiaires (EGB). The aim of this article is to describe the main characteristics of the SNIIR-AM and the EGB, to detail their accessibility according to French law, and to present their strengths and limits. It is illustrated with the most recent studies conducted in these databases. These databases include demographic, out-hospital reimbursement (including drug dispensing), medical (costly long-term diseases, occupational diseases, sick-leaves…), and in-hospital data. All these data are prospectively recorded, individualized, made anonymous and linkable. Consequently, the SNIIR-AM is a very useful data source for epidemiological, pharmacoepidemiological and health economics studies, particularly for rare diseases. The EGB is appropriate for long-term research on more frequent diseases.