Individuals with asthma living in the inner city experience increased asthma morbidity and mortality compared to the US average. The Controlling Asthma in America's Cities Project's Chicago site used a multifaceted approach to improve asthma care. The diverse scope of this project's interventions necessitated the use of novel methods to assess the effect of these interventions on the entire study area. Asthma-related medication-dispensing data were obtained from a large pharmacy chain for prescriptions filled in calendar years 2004-2006 for all individuals aged 5-17 years living in Chicago who filled at least four asthma-related medications within a 12-month period. Inhaled corticosteroid (ICS) use was considered inadequate if an individual had four or more dispensings of a short-acting beta-agonist without at least four dispensings of an ICS agent. Logistic regression was used to compare adequate ICS use in individuals within the intervention area with ICS use in the remainder of the city, after controlling for gender, insurance status, race, and poverty. A significant difference in adequate ICS use was found in years 2 (2005) and 3 (2006) of the project for individuals aged 5-9 in the intervention area (odds ratios for adequate ICS use-year 2, 1.26; CI, 1.04-1.53, p = 0.04; year 3, 1.30; CI, 1.08-1.55, p = 0.008) compared to individuals aged 5-9 in the remainder of the city. There was no similar significant difference in the 10-17 age group. These findings suggest an effect of a large multifaceted asthma intervention in improving medication use in the targeted age group. This methodology might also prove useful in the future for assessing the effect of similar interventions.