This study investigates the impact of measuring adherence and providing feedback on medication usage by children with unstable asthma. Adherence was measured using an electronic monitoring device. Subjects were randomized to either being told of their adherence during review consultations or for their adherence to remain undisclosed to their parents and treating physician. Subjects were reviewed monthly for 4 months. Twenty-six children aged between 6 and 14 years were recruited. Adherence was significantly higher in the intervention group (79% versus 58%, p <.01). There were significant improvements in clinical measures of disease control compared with baseline in both groups. The change in forced expiratory volume in 1 s (FEV(1)) (% predicted) was greater in those subjects receiving feedback (13.8% versus 9.8%). However, lung function values were lower in the intervention group at baseline and the relative improvement failed to reach statistical significance. Measuring adherence and providing feedback increases the use of preventive medication. A larger study is required to explore implications for disease control.