The aim of epidemiological studies is to determine the prevalence of particular health problems in a study group over a specific period. According to the World Health Organization (WHO), one in eight people worldwide suffer from mental disorders. There are many different types of mental disorders, including cognitive, psychotic, organic mental, emotional, behavioural regulation or personality disorders. The term personality is understood as a pattern of mental traits, automatically manifested in the psychological sphere of human functioning. In colloquial language, this term is sometimes used interchangeably with the concept of character and temperament yet, they actually have different meanings. Diagnosis of personality disorders is fraught with various problems and is often a time-consuming procedure. One of the problems is the difficulty in objectively distinguishing the norm from the pathology, which, on the one hand, makes it possible to overlook personality disorders and, on the other hand, to over-diagnose them.