Usual, normal emotions such as sadness, pain and joy are all part of our everyday lives and we should differentiate between them and pathological conditions or mood disorders. Affective disorders or mood disorders represent the most common group of mental disorders. Their fundamental characteristic is pathological mood change. They significantly deplete all aspects of a patient’s personality along with the overall psychological and social functioning. By the year 2020 depression will have become the second most common disease in the world with respect to morbidity and mortality (World Health Organization), and by the year 2030 the leading cause of disease burdens in affluent countries. The etiology of mood disorders is multifactorial and is the result of interaction between genetic predisposition, biological basis and an early life (traumatic) experience along with the impact of the surrounding circumstances. The typical difficulties and the most conspicuous features of depression are sadness, dejection, moodiness, weakness, listlessness, lack of incentive, self-doubt, feelings of worthlessness, hopelessness, futility. Along with them, often appear anxiety and restlessness, lack of energy, appetite disturbance, loss of body weight, decreased libido, sleep disorders, aches, poor concentration and suicidal thoughts. Mood disorders are diagnosed based on patient’s medical history, the clinical picture and the progress of the disease. In the treatment of mood disorders the best results are achieved by the combination of pharmacological and psychological therapy. The aim of the treatment is: diminish or eliminate symptoms, increase physical abilities and the general functioning of a patient, and reduce the possibilities of a relapse or recurrence of the disease. The nurse is often the first expert who contacts with patients. She participates intensively in the overall rhythm of a patient’s life. She is the closest person that patients and their families are in contact with so she is the first who is able to observe the changes and present her observations to the professional team, which are very important before proceeding. Therefore, the nurse’s therapeutic action is extremely important. She is a necessary and indispensable member of the team in a psychiatric care unit. The proof of the suffering of depressive patients can be found in this saying: "If there is a hell on Earth, then it is in the soul of a depressed person."