The elderly is usually recognized as an immunocompromised host. But physiologic age and chronologic age are not always concordant and there is the heterogeneity of older persons. Because of the atypical clinical presentation of infectious disease in the elderly, diagnosis is frequently difficult and treatment is delayed and the risk of developing or dying from most serious infectious diseases is usually increased in the elderly. The apparent risk factors associated with infectious diseases in the elderly are low nutrition, baseline diseases, swallowing disturbance and diminished cell mediated immunity. The primary objective in preventing and treating infectious diseases in the elderly are maintenance of the general condition and nutrition and to give rapid, short-term and adequate antibiotics treatment.