Use of a drug outside the terms of its official labelling is referred to as off-label prescription. Many categories of use exist because labelling of anticancer agents is very precise in terms of type or subtype of tumour, association, line, and duration of treatment. Off-label prescription of anticancer drugs is thought to be frequent but, in fact, very few surveys have been done to ascertain its real extent. Findings of prospective studies undertaken between 1990 and 2002 showed proportions of off-label drug use in children and adults of 6.7-33.2%. Most off-label prescription was reported in patients treated with palliative intent, some was associated with clinical benefits, and in specific cancers it formed the standard of care. Off-label use can lead to reimbursement restrictions. Regulatory agencies have created incentives to extend indications for approved drugs to remove them from the off-label area. Proposals have also been made to gather and disseminate accurate and unbiased information on off-label use and to record unapproved indications.