Objectives: To assess the feasibility and effectiveness of a general practice based, proactive system of asthma care in children. Design: Randomised controlled trial with cluster sampling by general practice. Setting: General practices in the northern region of the Australian Capital Territory. Participants: 174 children with moderate to severe asthma who attended 24 general practitioners. Intervention System of structured asthma care (the 3+ visit plan), with participating families reminded to attend the general practitioner. Main outcome measures: Process measures: rates for asthma consultations with general practitioner, written asthma plans, completion of the 3+ visit plan; clinical measures: rates for emergency department visits for asthma, days absent from school, symptom-free days, symptoms over the past year, activity limitation over the past year, and asthma drug use over the past year; spirometric lung function measures before and after cold air challenge. Results: Intervention group children had significantly more asthma related consultations (odds ratio for three or more asthma related consultations 3.8 (95% confidence interval 1.9 to 7.6; P = 0.0001), written asthma plans (2.2 (1. 2 to 4.1); P = 0.01), and completed 3+ visit plans (24.2 (5.7 to 103.2); P = 0.0001) than control children and a mean reduction in measurements of forced expiratory volume in one second after cold air challenge of 2.6% (1.7 to 3.5); P = 0.0001) less than control children. The number needed to treat (benefit) for one additional written asthma action plan was 5 (3 to 41) children. Intervention group children had lower emergency department attendance rates for asthma (odds ratio 0.4 (0.2 to 1.04); P = 0.06) and less speech limiting wheeze (0.2 (0.1 to 0.4); P = 0.0001) than control children and were more likely to use a spacer (2.8 (1.6 to 4.7); P = 0.0001). No differences occurred in number of days absent from school or symptom-free day scores. Conclusions: Proactive care with active recall for children with moderate to severe asthma is feasible in general practice and seems to be beneficial.