The value of obtaining children's reports about their health from questionnaires is a topic of considerable debate in clinical pediatrics and child health research. Evidence from the following areas can inform the debate: 1) studies of parent-child agreement or concordance about the child's health state, 2) basic research on the development of children's cognitive abilities, 3) cognitive interviewing studies of children's abilities to respond to questionnaires and of influences on their responses, 4) psychometric studies of child-report questionnaires, and 5) longitudinal research on the value of children's reports. This review makes a case for the utility of child rather than parent-proxy reports for many, though not all, applications. The review summarizes evidence in terms of the value and limitations of child questionnaire reports. Research demonstrates adequate understanding and reliability and validity of child reports of their health even at age 6, which increases after age 7 in general populations. The reliability of reports by children 8-11 years old is quite good on health questionnaires developed especially for this age group. Children's personal reports provide a viable means of monitoring internal experiences of health and distress during childhood and adolescence, which can enhance understanding about trajectories of health and development of illnesses.