The objective of this study was to develop a clinical asthma score (CAS) for use in hospitalized children between 1 and 5 years of age. Formal approaches to item selection and reduction, reliability, discriminatory power, validity, and responsiveness were used. The final CAS consisted of five clinical characteristics: respiratory rate, wheezing, indrawing, observed dyspnea, and inspiratory-to-expiratory ratio. Interrater reliability was high (weighted kappa = 0.82), and the CAS was discriminatory (Ferguson's delta = 0.92). The CAS was valid, with a strong correlation with length of hospital stay (Spearman's correlation = 0.47, p < 0.05) and drug dosing interval (Spearman's correlation = -0.58, p < 0.01). The CAS was responsive, with a significant change in CAS from admission to discharge (Wilcoxon signed rank test, p < 0.01). This score, for use in hospitalized preschool children, is reliable, discriminatory, valid, and responsive.