When everyday life becomes a burden... Often unrecognized or insufficiently acknowledged: fatigue in cancer patients. This tumor-associated pronounced exhaustion is one of the most common and particularly distressing side effects of cancer and its treatment. Its chronic course significantly reduces the quality of life for those affected, can lead to decreased treatment adherence, and may result in the discontinuation of therapy, as fatigue is often misinterpreted by patients as a progression of the cancer. Social and professional reintegration is also frequently impaired. How can fatigue be diagnosed and clearly distinguished from other disease symptoms? Which treatment strategies have proven effective? What preventive measures can be recommended to patients? For internists, oncologists, radiation therapists, radiologists, specialists, general practitioners, and nursing staff.