ABSTRACT Objective: to understand the professional practice challenges in reaching the goals and objectives of the National Patient Safety Program (Programa Nacional de Segurança do Paciente). Method: qualitative case study, based on the Comprehensive Sociology, carried out with 31 professionals from the Patient Safety Center (Núcleo de Segurança do Paciente) and the nursing team, working in a teaching hospital. Data collection took place between May and December 2015 through interviews, observation and documentary analysis. The analysis proceeded according to the prerogatives of the Content Analysis. Results: three categories emerged: the prescribed reality; material resources and their impact on care; and human resources related to the reality. Final considerations: challenges to safe professional practice are caused by inadequate physical structure, insufficient physical and human resources, but mainly invade the transition from the prescriptive reality scope.