All states of confusion with acute onset and alteration of thinking, perception and awareness are defined as "delirium". Delirium is a common problem in older patients admitted to the hospital. It is combined with a negative prognosis and complications (falls, infections, etc.). Diagnosis and management need special efforts. Delirium is mostly associated with an underlying disease. In the elderly patient, nearly every disease can be accompanied by delirium, and the fragile older patient is especially affected.Delirium should be evaluated using a systematic approach according to frequency and impact of possible causes. An accurate diagnosis can be challenging. Symptoms have to be distinguished from other cerebral alterations, such as preexisting dementia or depression. Due to the high prevalence, one should always be aware to the presence of delirium.With the treatment of the identified disease, there is generally a reduction of delirium. Often medical intervention in the acute state is necessary to prevent further alteration of the patient. Beside an adequate medical strategy, it is important to create a safe environment for the affected patient. The article gives suggestions for a systematic diagnostic and therapeutic strategy of delirium.