Mental disorders or mental illnesses are conditions that affect thinking, feelings, mood and behavior. They affect the quality of life, the ability to connect with other people, disrupt community life and daily functioning. They can be temporary or long-term when it comes to chronic mental illness. There is no defined cause of mental disorders, but they are contributed by a number of factors such as genes, life experiences, trauma, drug consumption or some biological factors such as chemical imbalances in the brain or psychological factors such as feelings of loneliness and sadness. Mental disorders in all European countries, including the Republic of Croatia, are the leading groups of diseases and therefore represent a priority of health challenges. They most often occur at a younger age, most often in adolescence, and it is estimated that every fourth person in the world will have some form of mental disorder. The types of mental disorders are different, and the most common are depression, eating disorders, psychotic disorders and anxiety disorders. Unfortunately, there are many misconceptions about mental disorders that are associated with a persons weakness, lack of strength, or even laziness. Mental disorders must be recognized and treated on time because in some cases they can lead a person to a state of hopelessness and eventually suicide. Therefore, the most important thing for a person suffering from any form of mental disorder is to provide support and help, not condemnation. The social worker has a key role in mitigating or eliminating problems that affect mental disorders. With his social approach, the social worker will indirectly and directly help people with mental disorders through various interventions: individual approach, family therapies, cooperation with various organizations and institutions and a number of other activities in prevention and education about mental disorders.