BACKGROUND: In clinical trials of asthma, the outcomes are often good, but when the same treatment regimens are implemented in primary care, equally good results are not obtained. Objective: To investigate if addition of structured patient information and monitoring by an asthma diary in primary care improves asthma control. METHODS: 141 patients from 19 primary care centres were studied. The centres were randomised to a standard care group or to an intervention group. The intervention group received structured written and oral information about asthma and asthma medication, and were instructed to keep an asthma diary. The primary outcome was asthma control as assessed by the Asthma Control Questionnaire. Secondary outcomes were costs of asthma medication, the Mini Asthma Quality of Life Questionnaire score and lung function. RESULTS: Asthma Control Questionnaire score changes differed between the study groups (p