Homeless children in New York City had an extremely high asthma prevalence-40%-in a cross-sectional study at 3 shelters (n = 740) during 1998 to 1999. We used the same protocol to summarize subsequent data through December 2002. Asthma prevalence was 33% (n = 1636); only 15% of the children previously diagnosed were taking an asthma controller medication. Emergency department use was 59%. These data were used to support a class action lawsuit that was resolved in favor of homeless children with asthma in New York City.