To evaluate the number of supervised gastrointestinal endoscopic procedures required to achieve initial competency using a simple objective grading system. Prospective, cross-sectional study. A gastroenterology and surgical training program at a large, university-affiliated county hospital. Seven gastroenterology fellows and five fourth-year surgery residents. Trainees were graded postprocedure using a microcomputer program. Grading criteria for esophagogastroduodenoscopy included entering the esophagus (esophageal intubation), traversing the pylorus into the duodenum, and recognizing whether the upper gastrointestinal tract was abnormal. Criteria for colonoscopy were traversing the splenic flexure, intubating the cecum, and recognizing whether the colon was abnormal. When presented with a case mix representative of practice, esophageal intubation did not reach 90% until more than 100 procedures had been done. Cecal intubation remained at only 84% after 100 procedures. More than 100 supervised upper gastrointestinal endoscopies or colonoscopies are necessary to achieve technical competence in gastrointestinal endoscopy.