The objective of this study was to review the development of a multidisciplinary asthma disease management program in a large medical group practice in an urban area, and evaluate the impact of the program on processes of care and health care utilization for adults and children with asthma. The disease management intervention included the development of a patient registry, a systematic approach to assessment of asthma control using the Asthma Therapy Assessment Questionnaire (ATAQ), case management, and physician education. An administrative database was used to examine hospital admissions and emergency department (ED) visits. A medical record audit was conducted to examine recorded compliance with asthma guidelines and documentation practices. The baseline study population included 3486 adults and children with asthma. The ATAQ suggested that, at baseline, control problems were frequent, with 34% of adult respondents missing work because of asthma. ATAQ also revealed several areas for care improvement. For example, only 20% of adult respondents reported having a written treatment plan. The chart review and administrative claims analyses showed that the program had beneficial results in several areas. Medical record documentation improved for asthma diagnosis (83.3% vs. 98.6%; p < 0.001) and patient education (15.7% vs. 26.1%; p < 0.001). No improvements were seen in documentation of peak flow ownership/use, smoking cessation advice, or influenza vaccination. ED visits related to asthma decreased from 148 per 1000 to 88 per 1000 (p < 0.001), and hospitalizations related to asthma decreased from 81 per 1000 to 37 per 1000 (p < 0.001). The outcomes suggest that this program was associated with a marked reduction in rates of hospitalization and ED usage for asthma, as well as significant improvement in several essential processes of care.