Elderly represent a large and increasing segment of the population worldwide. Susceptibility to infection in this period of life is substantially increased. The reasons for more frequent infections include impairment of immunity, reduction of physiologic functions, increased prevalence of chronic diseases associated with infections, the use of immunosuppressive drugs, and living in community. Clinical manifestation of an infection may be altered: symptoms and signs may be atypical, masked or even absent. Certain infections occur more often in elderly persons, and morbidity and mortality from infection are also higher that they are in younger adults. The three most commonly encountered types of infections are: urinary tract infections, respiratory tract infections, and skin and soft tissue infections. However, sepsis, intra-abdominal infections, infective endocarditis, bacterial meningitis, tuberculosis, and herpes zoster have a special predilection for elderly persons. Residents of long-term care facilities are highly vulnerable to infections. When prescribing antimicrobials for an elderly patient the age-related changes of the pharmacokinetics and pharmacodynamics of drugs has to be considered.