Late effects of treatment in children diagnosed and treated for brain tumours in infancy is a major concern. Assessment of infants presenting with brain tumours is difficult and there is little information available regarding the development of infants prior to treatment and hence the impact of the tumour itself on developmental outcomes.To describe the development of children diagnosed with brain tumours in infancy and to document their cognitive and adaptive function at school entry.Infants were psychologically evaluated at the time of diagnosis of a brain tumour and during their fifth or sixth year in preparation for school entry.Children diagnosed with brain tumours in infancy display developmental delays in a number of areas of adaptive function. By the time these children are school age they display further compromise in cognitive and academic skills and adaptive behaviour. Higher levels of deficit at follow-up were associated with tumour location in the supratentorium, younger age at diagnosis and longer time since diagnosis. The effect of radiotherapy could not be determined because of differing degrees of developmental compromise in the treatment groups at baseline.Brain tumours in infancy confer a risk of poor developmental progress at the time of diagnosis. These children display additional compromise of development by the time they reach school age. Research protocols evaluating the impact of treatment in infants diagnosed with brain tumours need to take account of the developmental status of the child at diagnosis.