Self-management of asthma and self-treatment of exacerbations are considered important in the treatment of asthma. For successful self-treatment, medication has to be inhaled correctly, but the percentage of patients inhaling effectively varies widely. As part of a self-management program we checked and corrected inhalation technique. This paper addresses differences among inhalers in relation to patient characteristics and the effect of instruction, 1 year after enrollment. Maneuvers that are essential for adequate inhalation were identified. When errors in inhalation technique were observed, patients were instructed in the correct use of their devices. One year later, inhalation technique was checked again. Only patients who used the same inhaler throughout the entire study period were analyzed. Of the 245 adult asthmatic patients who were enrolled in the self-management program, 166 used the same inhaler throughout the study period. One hundred twenty patients (72%) performed all key items correctly at baseline and this increased to 80% after 1 year. At follow-up, older patients were less likely to demonstrate a perfect inhalation. Patients with a Diskhaler(r) made fewest errors. Adjustment for differences in patient characteristics did not significantly change the results. Because many patients with asthma use their inhaler ineffectively, there is a need to know which inhaler leads to fewest errors. Diskhaler was nominated by this study. When patients are not able to demonstrate adequate inhalation technique in a “tranquil” setting, it is doubtful that they can do so when they experience an exacerbation. Therefore, inhalation instruction should be considered an essential ingredient, not only of self-management programs, but also of asthma patient care in general.