OBJECTIVE: To examine incidence, demographic risk factors, and patterns of injury resulting from falls from buildings and structures in areas with and without a legislation based prevention programme. DESIGN AND SETTING: The Health Care Cost and Utilization Project (KID-HCUP) was used to produce national estimates of hospital admissions due to falls from buildings in the US. Areas of New York with and without window guard legislation were identified through the New York Statewide Planning and Research Cooperative System (SPARCS). SUBJECTS: Children and adolescents aged 0-18 years. INTERVENTIONS: Legislation based window fall prevention programme with enforcement. MAIN OUTCOME MEASURES: Hospitalization for injury as a result of falls from buildings and structures in areas with and without enforced mandatory window guard legislation. RESULTS: New York City has a higher proportion of the population residing in multi-family dwellings with 10 or more units compared with the nation (53.8% v 12.6%, p<0.0001), but the incidence of injury resulting from falls from buildings is nearly half that observed in the US. For young children, warm weather risks begin earlier and extend later than previously reported. Incidence in very young minority children is nearly twice that of whites. Nearly 90% of children aged 0--4 years fall at home, but the proportion decreases linearly with age. CONCLUSIONS: Window guards are associated with reduced injury resulting from falls from buildings and should be mandated in multi-family dwellings where small children reside. Prevention programmes for young children should be initiated in early spring and continued through fall.