Objectives: Urban, African-American youth, aged 15-19 years have asthma fatality rates that are higher than Caucasians and younger children, yet few programs target this population. Traditionally, urban youth are thought to be difficult to engage in health-related programs, both in terms of connecting and convincing. We developed a multimedia, web-based asthma management program to specifically target urban, high school students. The program uses "tailoring", in conjunction with theory-based models, to alter behavior through individualized health messages based on the user's beliefs, attitudes, and personal barriers to change. Methods: High school students reporting asthma symptoms were randomized to receive the tailored program (treatment) or access generic asthma websites (control). The program was made available on school computers. Functional status and medical care use were measured at study initiation and 12 months post-baseline, as were selected management behaviors. The intervention period was 180 days (calculated from baseline). Results: A total of 314 students were randomized (98% African-American, 49% Medicaid enrollees, mean age=15.2 years). At 12 months, treatment students reported fewer symptom-days, symptom-nights, school days missed, restricted activity days, and hospitalizations for asthma when compared to controls; adjusted Relative Risk and 95% confidence intervals=0.5(0.4-0.8), p=0.003; 0.4(0.2-0.8), p=0.009; 0.3(0.1-0.7), p=0.006, 0.5(0.3-0.8), p=0.02, and 0.2(0.2-0.9), p=0.01, respectively. Positive behaviors were more frequently noted among treatment students compared to controls. Cost estimates for program delivery were $6.66/participating treatment group student. Conclusions: A web-based, tailored approach to changing negative asthma management behaviors is economical, feasible and effective in improving asthma outcomes in a traditionally hard-to-reach population.