Data from a cross-sectional community survey of 2852 children were used to provide estimates of the prevalence of a 'DSM-III-like' major depressive syndrome in children aged 6 to 16. The severity of symptoms required to define a 'case' was varied to generate three levels of diagnostic certainty (DC). The overall estimates of prevalence made with high DC were 0.6% for pre-adolescents and 1.8% for adolescents. Corresponding rates determined with medium DC were 2.7% and 7.8%, whereas the figures for low DC were 17.5% and 43.9%. Utilisation of mental health and social services, comorbidity (combined disorders), poor school performance, problems in getting along with others and need for professional help all increased as diagnostic certainty increased. There was wide disagreement in data supplied by the different groups of respondents, i.e. parents, teachers and adolescents.