The general aim of this study is to assess the relationships between external and internal auditors concerning cooperation and trust as resources integrated in organizations' lines of defense, to favor solid, opportune, and transparent decision‐making in organs of governance. More precisely, the specific aims are: (1) to analyze the relationship between trust and cooperation; (2) to explore and analyze the categories of the mutually important factors for trust and cooperation; and (3) to analyze the differences between internal and external auditors. To achieve these goals, quantitative and exploratory research was undertaken, with data collection through surveys directed to the two auditor groups (internal and external) in Portugal. In order to analyze if there were relations between trust and cooperation, logistic regression was performed. Based on exploratory factor analysis of principal components, it was possible to extract three factors for cooperation and trust: (1) work performance, (2) coordination/collaboration, and (3) competence. A multiple linear regression was also used to check the differences between internal and external auditors for the three factors identified. From the two groups involved in this study, it was possible to gain each group's perception of the professional relationship concerning cooperation and trust as determinant variables in auditing. It was found that there is still a long way to go and that each group has slightly different perceptions. This study contributes to the scientific and professional community regarding the perception of cooperation and trust between these professionals.