The FCCSS cohort (French childhood cancer survivor study) began in 1985. It was first called “Euro2K” because it included people treated in France and the UK. The Euro2K study included patients diagnosed before 1986 for a childhood cancer in five French cancer centres (3,300 people) and three British centres (1,200 people). From 1995 to 2005, analyses were conducted based on data from these 4,500 patients. They dealt with the risk of developing a second cancer, particularly focusing on the role of radiation therapy. Between 2005 and 2010, a questionnaire on their social, economic and medical outcomes was sent to the people of the “Euro2k” cohort, whose addresses were known or could be extracted from the RNIAM. Access to this directory was authorised by a ministerial decree in 2003. Overall, the addresses of 2,647 people were found. Among the 2,471 people contacted, 1,920 responded to the questionnaire (participation rate: 78%). Since 2012, the Euro2K cohort has grown to become the FCCSS (French childhood cancer survivor study). The cohort now includes patients who were treated for childhood or adolescent cancer before 2000, in thirty paediatric oncology services in France. The FCCSS study concerns only people treated for solid tumours or lymphoma. People treated for leukaemia are followed within the LEA cohort study.