The treatment of chronic mild to moderately severe asthma is expensive for families and for society. Controlling the costs of asthma-related medications, physician visits, emergency room visits, and hospital admissions is therefore an important consideration. A retrospective, record-based study was undertaken to determine the costs of treating asthma in patients for whom cromolyn sodium was included in the routine treatment plan (n = 27) and those for whom treatment did not include cromolyn sodium (n = 26). Significant reductions in the number of emergency room visits and hospital admissions were obtained in patients who were treated with cromolyn sodium. The estimated average cost of emergency room visits was $33 a year for the patients given cromolyn sodium compared with $624 a year for patients in the comparison group. The estimated average cost of hospital admissions was reduced by $1,298 for the cromolyn sodium group compared with a $357 reduction for the comparison group. Computed for the entire course of treatment, the average (+/- SD) daily cost of medications for the comparison group was $0.84 +/- $0.37 versus $0.93 +/- $0.25 for the cromolyn sodium treatment group. Thus dramatic savings in costs of emergency room visits and hospitalizations when cromolyn sodium was included in therapy were effected at a small increase in the overall cost of medications. Analyzed visit by visit, the average daily cost of treatment that included cromolyn sodium decreased while that of the comparison group increased. We conclude that including cromolyn sodium in a regular anti-asthma regimen is a cost-effective and therapeutically effective treatment strategy.