In a prospectively recruited random sample of adults with asthma, we ascertained symptom control and measured health-related quality of life using a generic (EuroQol five-dimensional questionnaire [EQ-5D]) and a disease-specific (Asthma Quality of Life Questionnaire) instrument, to estimate EQ-5D and five-dimensional Asthma Quality of Life Questionnaire (AQL-5D) utilities, respectively. We measured the adjusted difference in utilities across symptom control levels and calculated the loss of predictive efficiency due to aggregating multiple symptoms into one symptom control variable.