A 6-week surveillance study was performed to determine the prevalence of Stenotrophomonas maltophilia intestinal colonization among patients hospitalized in an oncology unit who developed diarrhea. Ninety-two stool samples obtained from 41 patients were cultured, and 4 patients (4 [9.5%] of 41 patients) had cultures that were positive for S. maltophilia. After controlling for duration of diarrhea, patients colonized with S. maltophilia had received a greater number of different types of antibiotics than noncolonized patients (5 vs. 3 different drugs; P=.04).