Antibiotic treatment of elderly patients implies special problems because of higher probability of reduced renal or other organ function, and interactions with other medications. Elderly patients are more often previously hospitalised and treated with antibiotics or live in health-care institutions, and may be colonised with resistant microorganisms. It is crucial to sample for microbiological diagnostics before therapy. Adverse effects of antibiotics are seen more frequently with increasing age. Otherwise, the effect of antibiotics and durations of therapy is independent of patient age.