Summary: Geriatric patients are a group particularly vulnerable to side effects resulting from polytherapy. It is associated, inter alia, with multiple diseases, impairment in drug absorption, distribution and metabolism. One of the often undiagnosed and potentially life-threatening complications of pharmacotherapy in elderly is serotonin syndrome. The causes of serotonin syndrome include drug interactions, accidental or deliberate overdoses, or combinations of drugs with serotonergic potential. Diagnosis is based on clinical signs. Key elements in recognition of serotonin syndrome are exposure to serotoninergic agents, appearance of neurological symptoms and rapid increase in temperature above 38°C. Particular attention should be paid to differential diagnosis. Early diagnosis, discontinuation of serotonergic drugs, and normalization of vital functions are the most important aspects treatment.