Objective: This study aimed to assess the degree of implementation and barriers encountered in the use of a practice guideline for optimal symptom relief for patients with dementia and pneumonia in Dutch nursing homes. Methods: A process evaluation included assessment of reach, fidelity, and dose delivered using researcher's observations, and dose received was addressed in a question “use of the practice guideline,” which the physicians completed for each patient included in the study. Perceived barriers were assessed with a structured questionnaire (response 69%) and semi-structured interviews (n = 14), which were subject to qualitative content analysis. Results: Of the 55 physicians involved in the intervention phase, 87% attended an implementation meeting; 20 physicians joined the study later (reach). The intervention was implemented as planned, and all intervention components were delivered by the researchers (fidelity and dose delivered). Thirty-six physicians included 109 patients. For 81% of the patients, the treating physician stated to have used the guideline (dose received). The guideline was perceived as providing a good overview of current practice, but some physicians had expected a more directive protocol or algorithm. Further, recommended regular observations of symptoms were rarely performed. Physician's often felt that “this is not different from what we usually do,” and with the acute illness, there was not always enough time to (re)familiarize with the contents. Conclusions: The physicians used the practice guideline frequently despite important barriers. Future implementation may involve strategies such as multiple interactive meetings. Further, the greatest potential to alter usual practice should be emphasized, such as using observational instruments.