Objectives:Before drawing conclusions on the contribution of an effective intervention to daily practice and initiating dissemination, its quality and implementation in daily practice should be optimal. The aim of this process evaluation was to study these aspects alongside a randomized controlled trial investigating the effects of a multidisciplinary biannual medication review in long-term care organizations (NTR3569).Design:Process evaluation with multiple measurements.Setting:Thirteen units for people with dementia in six long-term care organizations in the Netherlands.Participants:Physicians, pharmacists, and nursing staff of participating units.Intervention:The PROPER intervention is a structured and biannually repeated multidisciplinary medication review supported by organizational preparation and education, evaluation, and guidance.Measurements:Web-based questionnaires, interviews, attendance lists of education sessions, medication reviews and evaluation meetings, minutes, evaluation, and registration forms.Results:Participation rates in education sessions (95%), medication reviews (95%), and evaluation meetings (82%) were high. The intervention's relevance and feasibility and applied implementation strategies were highly rated. However, the education sessions and conversations during medication reviews were too pharmacologically oriented for several nursing staff members. Identified barriers to implementation were required time, investment, planning issues, and high staff turnover; facilitators were the positive attitude of professionals toward the intervention, the support of higher management, and the appointment of a local implementation coordinator.Conclusion:Implementation was successful. The commitment of both higher management and professionals was an important factor. This may partly have been due to the subject being topical; Dutch long-term-care organizations are pressed to lower inappropriate psychotropic drug use.