Chronic fatigue is one of the most common symptoms in primary care. This article is an overview of chronic fatigue and its syndromes (CFS) based on evidence-based clinical practice. The diagnosis of CFS relies on clinical evidence and exclusion of alternative medical or psychiatric diseases. The symptoms may overlap with depression, irritable-bowel-syndrome and fibromyalgia. The symptoms are thought to be the result of a disturbed psycho-neuro-immunological function but the underlying pathophysiology is not known. No medication has yet been shown to provide long-term remission or ”cure” for patients with CFS. Medication is used to relieve distress and promote quality of life. Cognitive-behavior treatment and graded exercise may be effective for some patients with CFS. Non-specific and medically unexplained illnesses are common in practice. To provide patients with comprehensive and efficient treatment, physicians should facilitate knowledge of stress-related health problems and explore high risk patients using bio-psycho-social models.