Objective. To test the feasibility, effectiveness, and sustainability of a pharmacy asthma service in primary care. Methods. A pragmatic cluster randomized trial in community pharmacies in four Australian states/territories in 2009. Specially trained pharmacists were randomized to deliver an asthma service in two groups, providing three versus four consultations over 6 months. People with poorly controlled asthma or no recent asthma review were included. Follow-up for 12 months after service completion occurred in 30 of randomly selected completing patients. Outcomes included change in asthma control (poor and fair/good) and Asthma Control Questionnaire (ACQ) score, inhaler technique, quality of life, perceived control, adherence, asthma knowledge, and asthma action plan ownership. Results. Ninety-six pharmacists enrolled 570 patients, with 398 (70 ) completing. Asthma control significantly improved with both the three- and four-visit service, with no significant difference between groups (good/fair control 29 and 21 at baseline, 61 and 59 at end, p = .791). Significant improvements were also evident in the ACQ (mean change 0.56), inhaler technique (17-33 correct baseline, 57-72 end), asthma action plan ownership (19 baseline, 56 end), quality of life, adherence, perceived control, and asthma knowledge, with no significant difference between groups for any variable. Outcomes were sustained at 12 months post-service. Conclusions. pharmacy asthma service delivered clinically important improvements in both a three-visit and four-visit service. Pharmacists were able to recruit and deliver the service with minimal intervention, suggesting it is practical to implement in practice. three-visit service would be feasible and effective to implement, with a review at 12 months.