In a general practice based population 76% of 530 children inhaling asthma medication inhaled correctly. However, important differences among inhalers were found. Children with a pressurized metered-dose inhaler without a spacer device performed worst, with only 22% inhaling without essential errors. At a second evaluation of the inhaler technique, one year after the first assessment, performances with a new device were more often incorrect versus the unchanged devices (21.1% and 10.8%, respectively; p = 0.01). Providing children with a new device should be carefully controlled over time especially because these children are error prone.