A self-efficacy scale for children and adolescents with asthma between 10 and 18 years of age is described. A scale of 38 items was constructed and administered to 60 children and adolescents. A factor analysis of the results yielded a scale consisting of 22 items which can be divided into three subscales: factor one (24.8% of variance) measured efficacy expectations concerning medical treatment, factor two (10.3% of variance) measured efficacy expectations concerning the environment, and factor three (6.7% of variance) measured efficacy concerning problem-solving skills. Confirmation of several predicted conceptual relationships between the self-efficacy measures and other measures (Personality Questionnaire, Coping, Anxiety, Knowledge, Optimism, and Shame) provided preliminary evidence of construct validity. Further research and clinical applications are discussed.