The overall incidence of nosocomial infections in children ranges from 2.3% to 12.6%. Even if there are great variations among data in literature, most authors agree that nosocomial infections are less frequent in children than in adults. Differences between these two populations concern anatomical sites of infection and microrganisms: in children, most frequent are gastrointestinal infections (10-35%), respiratory infections (5-30%) and bacteremia (10-23%); Gram positive bacteria account for 31-50% of infections, Gram negative for 23-35% and viruses for 22-27%. All these percentages change enormously depending on the type of department and child age. Because of increasing rates of resistance to antimicrobial agents, it is important to identify the main infectious agents and their sensibility, considering carefully when to give antibiotic therapy and what drug should be chosen.