Fatigue, as a common but non-specific medical complaint, is one of the most challenging symptoms to doctors in general medicine. At the same time, it is a symptom that accompanies many psychiatric and physical illnesses and that effects the process of treatment negatively. In patients with non-specific fatigue complaint, the lack of any sign in medical examination and laboratory tests may cause serious difficulties when approaching these patients. Patients with fatigue as a complaint are usually consulted to psychiatry, when routine examinations fail to find an organic cause. This may be unpleasant for patients and cause burden to psychiatrist, who fail to find any specific psychiatric disorder. Thus, fatigue may cause some negative effects on individual's functioning and quality of life. In this paper, concept of fatigue is discussed with a general point of view, medical history, clinical features of patients with fatigue, etiopatogenesis and treatment approaches are reviewed.