Delirium is an acute confusion state of multifactorial genesis, commonly seen in the elderly with multimorbidity. Age and dementia, followed by infections and polypharmacy, are known as the most important risk factors. Increased disease interactions and medication use in the multimorbid elderly might precipitate delirium. Serious consequences of multimorbidity often are psychiatric diseases such as depression. Also anxiety and schizoprenia show a high comorbidity with somatic diseases. The therapy of elderly multimorbid patients is risky and must be preceded by profound assessment of all pathogenic factors. Pharmacotherapy needs an ongoing screening for side effects and indication.