We reported increased rates of childhood asthma and worsening of preexisting asthma in Chinatown near the World Trade Center (WTC) after September 11, 2001. This conclusion was corroborated by the WTC Health Registry in 2003, which showed asthma prevalence in children <5 years old was higher than national estimates. In 2002, ethnic Chinese in New York City (NYC), based on 2000 U.S. Census addresses, were reported to have the lowest levels of asthma compared with other ethnic NYC neighborhoods. This study was designed to determine if Chinatown asthma rates are still higher than other ethnic neighborhoods and if rates decreased since 2003. We surveyed 353 parents of children at a Chinatown elementary school, conducted spirometry on 202 students, measured air pollution (PM2.5), and sampled dust from the floor of the school during 2008 for concentrations of dust-mite antigens, cat, rat, mouse, and cockroach. Asthma rates of 14.4% were reported in children who refused spirometry if they lived <1 mi from the WTC. The rate was 4.9% if they lived farther away. Twenty-nine percent of all students (4-12 years old) who had spirometry showed a forced expiratory volume at 1 second (FEV(1)) of <80% predicted normal. Among children who were alive in 2001, 17.4% had an FEV(1) of < or = 75% predicted. The concentration of PM2.5 reached a high level of 40 microg/m(3). Indoor aeroallergen concentrations were negligible. Chinatown asthma rates are still higher than among other groups (29% versus the NYC reference rate of 13%). High air pollution levels may account for increased asthma incidence. It is possible that exposure to toxins on September 11, 2001 accentuated the effect of subsequent exposure to air pollution.