Objective To assess any improvements in knowledge of asthma patients after a tailored education program delivered by pharmacists and measure the sustainability of any improvements. To ascertain patients' perceptions about any changes in their knowledge. Methods Ninety-six specially trained pharmacists recruited patients based on their risk of poor asthma control. A tailored intervention was delivered to patients based on individual needs and goals, and was conducted at three or four time points over six months. Asthma knowledge was assessed at the beginning and end of the service, and six and 12 months after it had ended. Patients' perceptions of the impact of the service on their knowledge were explored qualitatively in interviews. Results The 96 pharmacists recruited 570 patients, 398 (70%) finished. Asthma knowledge significantly improved as a result of the service (7.65 ± 2.36, n = 561, to 8.78 ± 2.14, n = 393). This improvement was retained for at least 12 months after the service. Patients reported how the knowledge and skills gained had led to a change in the way they managed their asthma. Conclusion Improvements in knowledge are achievable and sustainable if pharmacists used targeted educational interventions. Practice implications Pharmacist educational interventions are an efficient way to improve asthma knowledge in the community.