During a four-month period, Salmonella typhimurium developed in seven persons within five days of fiberoptic upper gastrointestinal (GI) endoscopy. A retrospective cohort study confirmed the association between S typhimurium infection and fiberoptic upper GI endoscopy. Salmonella typhimurium was cultured from the endoscopic equipment and the accessory suction equipment. The Salmonella isolated from the endoscopic and accessory suction equipment was identical to that recovered from the seven patients with salmonellosis by serotype, antimicrobial susceptibility pattern, and bacteriophage lysis pattern. Salmonella transmission was attributed to inadequate disinfection of the endoscope and accessory equipment between procedures. The original source of the contamination was not discovered.