Hospital acquired infections are one of the most serious problems of public health. The problem of hospital infections assumes greatest relevance especially for patients in intensive care units (ICU). In these patients both the incidence (about 40%) and the mortality rate (non infected patients 13%; infected patients 47%) of infections is particularly high. Low respiratory tract represents the most frequent localization of ICU infections (30-50%). The causal pathogens are represented in more than 50% of cases by Gram-negative bacilli provided with low virulence and normally present in patients and in the hospital environment. The pathogenesis of infections in ICU is multiform, deriving from the interplay of many factors: the impairment of organic defenses; the age of the patients, often at the upper or lower limits; the multi-pathology and severity of underlying disease; the side effects of medical therapy (immunodepression); the closeness of many patients in narrow wards, that allows the diffusion of infections; the presence in the hospital environment of many pathogens with poly-antibiotic resistance. The control and prophylaxis programs should include: interventions on ICU structure in order to optimize the building projects and maintain high standard quality; training programs for medical and nursing personnel; interventions on patient-related factors; surveillance protocols (events documentation and monitoring of intervention results).