The Childhood Asthma Management Program (CAMP) is a multicenter, randomized, double-masked clinical trial designed to determine the long-term effects of three inhaled treatments for mild to moderate childhood asthma: budesonide (a glucocorticoid used daily) and albuterol (a short-acting beta-agonist bronchodilator used as needed); nedocromil (a nonsteroid anti-inflammatory agent used daily) and albuterol; and placebo and albuterol. One thousand forty-one children (32% from ethnic minority groups), aged 5 to 12 years at screening, are currently participating. The primary outcome measure is lung growth as indicated by postbronchodilator forced expiratory volume in 1 second (FEV1) percent of predicted, observed over 5- to 6-year period. The trial also assesses differences between treatment groups with respect to airway responsiveness, morbidity, physical growth and development, and psychological growth and development. This report describes the design of the trial, the rationale for the design choices made, and the methods used to carry out the trial.