Stenotrophomonas maltophilia (formerly Xanthomonas maltophilia) is a gram-negative bacillus increasingly associated with serious nosocomial infections. Here, the case of a 69-year-old female patient who developed prosthetic valve endocarditis associated with this organism is described. A review of the literature revealed only 18 previous reports; eight involved native valves, the remainder prosthetic valves. Most cases were associated with risk factors, including intravenous drug abuse (6 patients), infected intravenous lines (4 patients) or a recent invasive procedure (3 patients). The course of the disease appears to be indolent, but is otherwise similar to infective endocarditis associated with other gram-negative organisms. Antimicrobial therapy is complicated by multiple drug resistance of the organism; cotrimoxazole may be beneficial, if the isolate is susceptible, in combination with another agent. Five of nine (55%) patients who underwent valve replacement survived, as compared to three of seven (43%) who received antibiotic therapy only. Hence, surgery is not essential for survival in every case and depends as much on the individual patient's course as on established criteria for valve replacement in prosthetic valve endocarditis.