Candida lusitaniae, a fungus with a low incidence of infection in immunocompetent people, is emerging as an opportunistic pathogen in immunocompromised hosts. This yeast is generally resistant to amphotericin B and may present therapeutic difficulties. C. lusitaniae may be misidentified as one of several other fungal species, including Candida tropicalis, Candida parapsilosis, and evenSaccharomyces cerevisiae. As judged by in vitro antifungal susceptibility testing, minimal inhibitory concentrations of antifungal agents other than amphotericin B are achievable, but fungicidal levels are not. When encountered in blood or other body sites, C. lusitaniae should be carefully considered as a potential pathogen.