Nosocomial infections (NI) still have a high incidence in intensive care units (ICUs), and are becoming one of the most important problems in these units. It is well known that these infections are a major cause of morbidity and mortality in critically ill patients, and are associated with increases in the length of stay and excessive hospital costs. Based on the data from the ENVIN-UCI study, the rates and aetiology of the main nosocomial infections have been described, and include ventilator-associated pneumonia, urinary tract infection, and both primary and catheter related bloodstream infections, as well as the incidence of multidrug-resistant bacteria. A literature review on the impact of different nosocomial infections in critically ill patients is also presented. Infection control programs such as zero bacteraemia and pneumonia have been also analysed, and show a significant decrease in NI rates in ICUs.