Accurate evaluation of asthma self-efficacy is essential to the effective management of asthma. This article describes the development and testing of the Asthma Belief Survey (ABS). The instrument is a 15-item tool that uses a 5-point self-report scale to measure asthma self-efficacy in relation to daily asthma maintenance and an asthma crisis. This instrument was tested with a sample of 79 African American school children, who attended eight inner-city elementary schools. The mean age of the sample was 11.05 years with a range of 8 to 14 years. The majority of students had been diagnosed with asthma prior to the age of 5 years. The Asthma Belief Survey demonstrated good psychometric properties: good Cronbach's alpha reliability coefficient (.83), coherence as a single scale measuring children's self-efficacy in treating their own asthma, and significant relationships with scales of asthma knowledge (r = .51, p < .000) and asthma self-care practices (r = .52, p < .001). The Asthma Belief Survey has sound reliability and validity evidence to support its use to measure a child's asthma self-management self-efficacy. The practitioner can use this instrument to assess a child's self-efficacy in the areas of asthma health maintenance and avoidance of asthma episodes.