The subject of the article is the problem of assessment errors and its consequences. The authors discusses the problem of the assessment process of employees, noting that assessment is one of the most widespread activities in the practice of the functioning of the company. This happens, among others, because the assessment of the employee’s work is the basis for many personnel decisions and is closely related to the performance of managerial functions. Next, the authors analyze the assessment system defining its features and the purposes of assessing employees from the point of view of the employee and the employer. They emphasize that a well-designed evaluation system is a great facilitation for the managerial staff as well as for employees, and should therefore be based on clearly defined rules and criteria. Finally, the authors present errors in the employee assessment process, because improper assessment can bring more harm than benefits. They emphasize that the probability of errors will be less when the whole process is prepared in terms of its substance, psychology and organization. In addition to good preparation, you also need a lot of responsibility from the assessors.