To determine the frequency and effects of and risk factors for fireworks-related injury, we identified all 146 persons who were injured by fireworks and sought emergency care during the 1983 July 4 holiday in the Seattle area. The mean charge for medical care for the injuries received was $562; 7.1% of those injured required hospitalization. In a matched-pair case-control study, use of either of two fireworks types—firecrackers or aerial devices—was significantly associated with injury (odds ratios [ORs], 3.3 and 2.9, respectively; 95% confidence intervals [CI], 1.2, 8.5, and 1.2, 6.6, respectively). Also associated with injury were several fireworks misuse behaviors, including lack of adult supervision of children (OR, 11.5; CI, 2.8, 100.6). We conclude that fireworks cause serious injuries that theoretically could be prevented by behavioral changes or decreased availability of high-risk fireworks devices.