During a 2-week period following the colonoscopy and biopsy of a patient with acute Salmonella newport gastroenteritis, S. newport was recovered from colonic aspirates or fecal specimens of eight of 28 patients from whom specimens were cultured during or after colonoscopy. Two of the eight persons from whom S. newport was isolated developed acute gastroenteritis, two had asymptomatic infections, and four had positive aspirates collected through a colonoscope but did not become infected. Although S. newport was never recovered from the four colonoscopes used during the outbreak, cultures of one of the colonic biopsy forceps grew S. newport. Contamination of the equipment most likely occurred during colonoscopy of the index patient. Inadequate disinfection of the equipment allowed the organism to survive and possibly to cross-contaminate other colonoscopes, and the organism was then transmitted to other patients by use of the contaminated colonoscopes or the contaminated biopsy forceps. Implemented control measures terminated the outbreak.