Evaluating the implementation of care models such as Primary Nursing requires assessment of both short-term and long-term outcomes. In a hospital in Piemonte, Italy, a mixedmethod time-series study was conducted to assess if and how the organizational culture of nurses changed in relation to the implementation of a new organizational model of care. Instruments used included the Condition of Work Effectiveness Questionnaire (CWEQ II) and an investigator-developed questionnaire to evaluate perceptions of dimensions consistent with Primary Nursing. Results showed a significant culture change over time related to the implementation of Primary Nursing, mainly in terms of nurses' understanding of their professional role specifications. In addition, the results supported a relationship between being involved in the project implementation and the procedural and cultural approach adopted.