The incidence of Candida spp is increasing in critically ill patients. The impact of the infection is briefly reviewed. Infections mainly evolve from endogenous colonization facilitated by the use of broad spectrum antibiotics; nosocomial exogenous transmission occasionally occurs, however. A complete understanding of the process of infection requires careful epidemiological investigation as well as the use of powerful laboratory tools that allow intraspecies delineation of Candida strains. The value of contour-clamped homogeneous field gel electrophoresis is discussed. Preventive treatments with antifungal agents will help to improve the outcome of severe infection, but still need to be evaluated in appropriately controlled clinical trials.