Objective: The main aim of this article is to present the negative impact of stress on the mental state of man, the associated negative effects resulting in considerable disorders in his well-being, especially threats to the functioning in the workplace. Substantive and cognitive resources of article are based on the identification of the sources and causes of stress, which mean the effectiveness of the stressors that significantly interfere with the ability to correct functioning of a person in the work environment. Attention was also drawn to the complicated structure of the stress, the causes of which are not related only to the nature and pathologies associated with the work and to unlawful influences of superiors, but also psychosomatic predisposition of employee. Introduction: Ensuring adequate psychological comfort of the worker is a very important requirement, because it is one of the main factors determining the proper and effective performance of duties. The correct activity which reduces the negative effects of mental discomfort, however, must precede by the identification of the sources, causes and stress levels in people suffering from this dysfunction, performing their duties, operating in different environments, mainly in the work, to ensure them the normal conditions for the harmonious development. Due to the fact that the largest range of negative effects creates work stress, this matter has been widely discussed. Methodology: The study used the method of descriptive analysis and examination of statistical data. PubMed, Medline database and available literature and yearbooks items were used. Conclusion: The stress that accompanies the man from almost always, can have a positive, motivating effect on the employee, but usually leads to complete organization disorder of the functioning. This is particularly evident in the case of permanent, severe stress, e.g. caused by mobbing, under which the worker is often in the work environment. The most common effect of this situation is reduced psychological comfort, which can also affect the health problems, absenteeism and reduce the efficiency of the work. The issue taken in the article presents data which show that one of the basic functions of executive’s bodies and management is the need to take action to minimize the level of stress in the workplace. It is undoubtedly necessary both for the protection of employee welfare, as well as create favorable conditions for the proper and efficient development of the company.