The possible transmission of pathogens to 236 persons exposed to an endoscope processed in a flawed automated endoscope washer-disinfector in a gastrointestinal endoscopy unit was investigated. During 6 months, 197 patients (83.5%) were followed up, and no cases of acute human immunodeficiency virus, hepatitis C virus, or hepatitis B virus infection were observed. This event created the conditions for improvements in safety procedures.