ENThe aim of the study is to investigate the impact of nepotism as a form of corruption on the effectiveness of organizations, determining the relationship between the manager and employees, employee relations, and taking it into account as a potential threat to secure and sustainable development of the organization and society. The data collected from private and public organizations were used to test research hypotheses. The AMOS version 26 program and structural equation modeling (SEM) were applied to check the models with median effects. The results of the test allowed to identify the negative aspects of nepotism in the relationship between the manager’s behavior and organizational performance. Nepotism causes internal conflicts and an atmosphere of mistrust in both public and private organizations, which leads to poor company performance and quality of services provided, and the potential loss of professionals. The results of the research show that the problem of nepotism is still relevant in Lithuanian society. The research results allow envisaging both systematic and ideological measures to prevent corruption in Lithuania. Models for the prevention of this form of corruption can be constructed on the basis of this research. Keywords: nepotism; corruption; public organizations; sustainable development; national security; SEM. [From the publication]