A nosocomial infection (NI) is an infection contracted in a hospital or other health-care facility. An essential requirement for the diagnosis of NI is the lack of evidence of infection (subclinical or within the incubation period) on admission to the hospital. The onset of a NI usually begins 48-72 hours after hospitalization or can be longer in infections with long or variable incubation period such as hepatitis or varicella. Owing to the number and constant variability of factors that contribute to the development and persistence of NIs within the hospital environment, these conditions represent an important public health issue. NIs add to the length of hospital stay, contribute to the economic burden for the family and the institution and are responsible for the increased mortality associated with hospitalization. Accordingly, hospital-acquired infections are a true challenge for both the treating clinician as well as health authorities and administrators of tertiary medical institutions. The introduction of new technologies, especially in PICU and NICU, health-care equipment and immune status characteristics are some factors related with the development of nosocomial infections. Indeed, the study of factors associated with these hospital-acquired infections is crucial for their prevention in our patients. Hand washing is the single most effective measure to prevent the development of NIs with great results. Cleaning of surfaces and recommendations for inanimate objects, health-care personnel education in aseptic technique practices and isolation measures are a part of goals to prevent the spread of nosocomial infections.