Abstract: Background In October 2013, a New Medicines Service (NMS) was introduced in community pharmacies in Belgium to support asthma patients who are novice users of inhaler devices with corticosteroids. The protocol-based intervention used the Asthma Control Test (ACT) and the Medication Adherence Report Scale (MARS) to assess asthma control and medication adherence. The NMS is the first initiative that puts advanced pharmaceutical care into practice in Belgium. The present study evaluated the degree to which the NMS program is delivered as intended, drawing on the concept of implementation fidelity (IF). Methods The main dimensions of IF and potential moderating and facilitating factors for the implementation of NMS in community pharmacies were evaluated using telephone interviews with pharmacists (n = 497), semi-structured interviews with patients eligible for NMS (n = 30), focus groups among general practitioners (n = 72) and lung specialists (n = 5), and a work system analysis in community pharmacies (n = 19). Results The uptake of NMS in Belgian community pharmacies remains low. In addition to practical barriers, pharmacists found it difficult to identify new asthmatic patients when they were not informed about the diagnosis. A lack of commitment from physicians, patients and pharmacists was noted in the early start-up phase of the program. Many pharmacists did not see how NMS differed from existing pharmaceutical care. Physicians considered this service as part of their own tasks and discouraged ACT for asthma follow-up in the community pharmacy. Conclusions The introduction of the NMS program was not sufficiently embedded in the Belgian health care organization, causing low uptake and resistance to its implementation by pharmacists, patients, and other health care professionals. To increase the uptake of this type of service and its possible extension to other patient groups, more collaboration among the different health care professionals during design and implementation is necessary, as well as ...