Objectives The pattern of autoimmune diseases in childhood cancer survivors has not been investigated previously. We estimated the risk for an autoimmune disease after childhood cancer in a large, population-based setting with outcome measures from comprehensive, nationwide health registries.

Methods From the national cancer registries of Denmark, Iceland and Sweden, we identified 20 361 1-year survivors of cancer diagnosed before the age of 20 between the start of cancer registration in the 1940s and 1950s through 2008; 125 794 comparison subjects, matched by age, gender and country, were selected from national population registers. Study subjects were linked to the national hospital registers. Standardised hospitalisation rate ratios (SHRRs) and absolute excess risks (AERs) were calculated.

Results Childhood cancer survivors had a significantly increased SHRR of 1.4 (95% CI 1.3 to 1.5) of all autoimmune diseases combined, corresponding to an AER of 67 per 100 000 person-years. The SHRRs were significantly increased for autoimmune haemolytic anaemia (16.3), Addison's disease (13.9), polyarteritis nodosa (5.8), chronic rheumatic heart disease (4.5), localised scleroderma (3.6), idiopathic thrombocytopenic purpura (3.4), Hashimoto's thyroiditis (3.1), pernicious anaemia (2.7), sarcoidosis (2.2), Sjögren's syndrome (2.0) and insulin-dependent diabetes mellitus (1.6). The SHRRs for any autoimmune disease were significantly increased after leukaemia (SHRR 1.6), Hodgkin's lymphoma (1.6), renal tumours (1.6) and central nervous system neoplasms (1.4).

Conclusions Childhood cancer survivors are at increased risk for certain types of autoimmune diseases. These findings underscore the need for prolonged follow-up of these survivors.