A high prevalence of suboptimal asthma control is attributable to known evidence-practice gaps. We developed a computerised clinical decision support system (the Electronic Asthma Management System (eAMS)) to address major care gaps and sought to measure its impact on care in adults with asthma.This was a 2-year interrupted time-series study of usual care (year 1) versus eAMS (year 2) at three Canadian primary care sites. We included asthma patients aged ≥16 years receiving an asthma medication within the last 12 months. The eAMS consisted of a touch tablet patient questionnaire completed in the waiting room, with real-time data processing producing electronic medical record-integrated clinician decision support.Action plan delivery (primary outcome) improved from zero out of 412 (0%) to 79 out of 443 (17.8%) eligible patients (absolute increase 0.18 (95% CI 0.14-0.22)). Time-series analysis indicated a 30.5% increase in physician visits with action plan delivery with the intervention (p<0.0001). Assessment of asthma control level increased from 173 out of 3497 (4.9%) to 849 out of 3062 (27.7%) eligible visits (adjusted OR 8.62 (95% CI 5.14-12.45)). Clinicians escalated controller therapy in 108 out of 3422 (3.2%) baseline visits versus 126 out of 3240 (3.9%) intervention visits (p=0.12). At baseline, a short-acting β-agonist alone was added in 62 visits and a controller added in 54 visits; with the intervention, this occurred in 33 and 229 visits, respectively (p<0.001).The eAMS improved asthma quality of care in real-world primary care settings. Strategies to further increase clinician uptake and a randomised controlled trial to assess impact on patient outcomes are now required.