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It has been proposed that infections in infancy and early childhood are associated with a reduced risk of childhood acute lymphoblastic leukaemia (ALL). We tested this hypothesis in a register-based study of hospitalisations for infectious diseases prior to diagnosis of childhood ALL.A nation-wide cohort encompassing all Danish children aged 0–14 years and born between 1977 and 2008 (N = 1,778,129) was established and followed for hospitalisations for infectious diseases and risk of childhood ALL. The exposure was lagged 1 year to limit reverse causality. In the statistical analyses exposure was defined as (time dependent) number of early or late (before 2 or at/after 2 years of age) hospitalisations to further explore possible age-dependent associations.A total of 815 children were diagnosed with ALL during follow-up. Risk of ALL was associated neither with hospitalisations for infectious diseases before (incidence rate ratio = 0.92, 95% confidence interval 0.78–1.07) nor at/after 2 years of age (incidence rate ratio = 1.04, 95% confidence interval 0.81–1.32). This also applied to subsets of ALL supposedly initiated prenatally.The absence of association between hospitalisation for infections and risk of childhood ALL directs future investigations of the role of infections in development of childhood ALL towards exploration of less severe infections. Pediatr Blood Cancer 2013; 60: 428–432. © 2012 Wiley Periodicals, Inc.