The Paediatric Asthma Quality of Life Questionnaire contains 23 items that children with asthma have identified as troublesome in their daily lives. The aim was to evaluate the measurement properties of the questionnaire. The study design consisted of a 9 week single cohort study with assessments at 1, 5 and 9 weeks. Patients participating in the study were fifty-two children, 7-17 years of age, with a wide range of asthma severity. At each clinic visit, a trained interviewer administered the Paediatric Asthma Quality of Life Questionnaire, the Feeling Thermometer, a clinical asthma control questionnaire and measured spirometry. For 1 week before each clinic visit, patients recorded morning peak flow rates, medication use and symptoms in a diary. The Paediatric Asthma Quality of Life Questionnaire was able to detect quality of life changes in those patients who altered their health status either as a result of treatment or natural fluctuations in their asthma (p < 0.001) and to differentiate these patients from those who remained stable (p < 0.0001). It was reproducible in patients who were stable (ICC = 0.95), which also indicates the instrument's strength to discriminate between subjects of different impairment levels. The questionnaire showed good levels of both longitudinal and cross-sectional correlations with the conventional asthma indices and with general quality of life. The results were consistent across individual domains and different age strata. The Paediatric Asthma Quality of Life Questionnaire has good measurement properties and is valid both as an evaluative and a discriminative instrument. It captures aspects of asthma most important to the patient and adds additional information to conventional clinical outcomes.