Objectives To evaluate (1) the state of the art in sustainability research and (2) the outcomes of professionals' adherence to guideline recommendations in medical practice. Design Systematic review. Data sources Searches were conducted until August 2015 in MEDLINE, CINAHL, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL) and the Guidelines International Network (GIN) library. A snowball strategy, in which reference sections of other reviews and of included papers were searched, was used to identify additional papers. Eligibility criteria Studies needed to be focused on sustainability and on professionals' adherence to clinical practice guidelines in medical care. Studies had to include at least 2 measurements: 1 before (PRE) or immediately after implementation (EARLY POST) and 1 measurement longer than 1year after active implementation (LATE POST). Results The search retrieved 4219 items, of which 14 studies met the inclusion criteria, involving 18 sustainability evaluations. The mean timeframe between the end of active implementation and the sustainability evaluation was 2.6years (minimum 1.5-maximum 7.0). The studies were heterogeneous with respect to their methodology. Sustainability was considered to be successful if performance in terms of professionals' adherence was fully maintained in the late postimplementation phase. Long-term sustainability of professionals' adherence was reported in 7 out of 18 evaluations, adherence was not sustained in 6 evaluations, 4 evaluations showed mixed sustainability results and in 1 evaluation it was unclear whether the professional adherence was sustained. Conclusions (2) Professionals' adherence to a clinical practice guideline in medical care decreased after more than 1year after implementation in about half of the cases. (1) Owing to the limited number of studies, the absence of a uniform definition, the high risk of bias, and the mixed results of studies, no firm conclusion about the sustainability of professionals' adherence to guidelines in medical practice can be drawn.