Most health-related quality-of-life measures make an assessment at a single point in time. Comparing results before and after an intervention is often difficult, because the difference measured is usually small compared with the variation between individuals. A retrospectively applied measure specifically worded to assess benefit would be very useful for clinical research. Such a measure exists for adults. We aimed to develop a similar measure for children. We chose potential items after reviewing existing health-related quality-of-life measures, published literature, and parental interviews. A draft questionnaire was given to a group of parents and modified. The resulting Glasgow Children's Benefit Inventory (GCBI) comprised 24 questions on the consequences of a specified intervention on various aspects of the child's day-to-day life, without reference to any specific symptoms, and was worded to apply to children of any age. The questionnaire was mailed to the parents of all 1,777 children who had undergone tonsillectomy or ventilation tube insertion at one hospital during the period January 1998 to December 2001. There were 670 questionnaires returned. The GCBI scores correlated well with parental satisfaction with surgery and with estimates of technical success (residual sore throats, reported hearing impairment, ear infections). The questionnaire had high internal consistency. Factor analysis showed 4 dimensions in the pattern of responses relating to emotion, physical health, learning, and vitality. The GCBI is a means to retrospectively assess benefit after an intervention in children, and we have shown initial evidence of reliability and validity. Although not restricted to any branch of pediatric medicine, it is eminently suitable for use in pediatric otolaryngology.