Acinetobacter baumannii has emerged as an important nosocomial pathogen. It is difficult to control and treat. The most seriously ill patients and those previously infected are more likely than others to be infected or colonized by A. baumannii. The epidemiology of A. baumannii infection is complex, with the coexistence of epidemic and endemic infections. The A. baumannii are the species isolated in 90% of the nosocomial infections and in 92% of the nosocomial bacteremias. The intensive care units presented the greater number of nosocomial bacteremias by A. baumannii. The most common sources of A. baumannii are respiratory tract, surgical wound, catheter, urinary tract and others. The most frequently clinical manifestation is sepsis and a fulminating course is observed when the patient presents septic shock. Progressive resistance of A. baumannii to antimicrobial limits the therapeutic options. The patients with A. baumannii multidrug-resistant present an excessive rate of attributed mortality, length of stay and costs.