A prospective survey of fecal, urinary tract, and environmental colonization by Providencia stuartii in two wards was undertaken over a 5-month period. Eight of 53 male patients and 2 of 89 female patients were colonized with the endemic serotype O:63. Two patterns of colonization were found on the male ward. Two patients had persistent urinary tract colonization with no detectable fecal carriage. The other patients had fecal carriage, in some cases persistent, with intermittent urinary tract colonization. The ward environment was in general not contaminated. This study demonstrates that fecal colonization of patients by P. stuartii may be an important and previously underestimated nosocomial reservoir.