Background: Shared decision-making (SDM) can be a way for staff to adopt international recommendations advocating the involvement of nursing home residents and their family members in care planning and the development of personalized care plans. Objective: The main aim was to analyze the effects of training nursing home staff in the implementation of SDM on agreement of residents' 'life-and-care plans' with the recommendations (primary outcome) and on family caregivers' quality of life and sense of competence, and staff's job satisfaction (secondary outcomes). Methods: In the intervention condition, staff attended a training program on the use of SDM with residents and family caregivers in the care planning process. In the control condition, care planning as usual took place. For the primary outcome, in-depth qualitative and quantitative analyses of the care plans were performed. Multivariate Permutation Tests were applied to assess the impact on secondary outcomes. Results: Forty-nine residents and family caregivers and 34 professionals were involved. Overall, many of the care plans developed during the intervention showed a high level of agreement with the care planning recommendations. Both Italian and Dutch care plans showed improvement in the number of clear problem statements (p < 0.001). In Italy, significant improvements (p < 0.05) were also found regarding specific care objectives, documentation of objectives met, and of residents and families' involvement. No impact was found on secondary outcomes. Conclusion: The involvement of residents and family caregivers in care planning contributed to an improvement of the residents' care plans, but it did not have an effect on family caregivers and staff outcomes.