The investigators propose a double-blind, randomized, placebo-controlled trial of azithromycin in children aged 4-12 years with persistent asthma hospitalized with acute asthma exacerbations. Children will be enrolled within 12 hours of admission and will be randomized to receive three days of either azithromycin or placebo suspension (10mg/kg/dose, max of 500mg). The primary outcome measure will be length of stay (LOS). Secondary outcome measures will include: days of school/work missed, readmission rates, return to medical care rates, recurrence of symptoms, and steroid courses. In the future, patients may also be approached to enroll in the "Mechanism Subset Study" a separate pilot and feasibility study which will require two blood samples and two nasal aspirate samples and will test for atypical pathogens, intraleukin-8 levels, and neutrophil/eosinophil counts. The average length of stay for patients in this age range with asthma in 2011 at our institution was 3.0 days. The investigators will enroll to achieve a power of 80%, with an alpha of 0.05, which will require 107 patients in each group to detect a 16 hour (0.67 day) difference in the primary outcome, LOS. We hypothesize that azithromycin treatment in children hospitalized with acute asthma will decrease LOS.