Nowadays in Brazil and throughout the world, transformation is one of the most striking characteristics. In the face of so many changes, organisations are faced with the need to seek solutions that increase their effectiveness and success in such a competitive market. The aim of this study is to present a reflection on current affairs, presenting leadership as one of the factors for organisations to achieve this success and emphasising the importance of an effective leader in motivating their team and achieving optimum results in the work carried out. The topics covered will be leadership styles, the differences between the main characteristics of leaders and bosses and the positive and negative points of each style. The central theme of this work is workers’ mental health and how organisational environments and their managers contribute to good or bad health. We seek to clearly present the extent to which work is beneficial in each individual’s life and when it becomes considered suffering, leading to psychological and depressive illnesses.