Two adult-size endoscopes (Olympus GIF-K2 and ACMI TX-8) were compared for extent of duodenal intubation by the endoscopist's estimate of location and x-ray position in 55 patients. The endoscopes were not different in duodenal position when separately analyzed for the endoscopist's estimate or x-ray location. Combining the results for both endoscopes showed the endoscopist's estimate to differ significantly from x-ray location in 47% of patients (p = 0.02). When incorrect, the endoscopist overestimated 62% of the time and underestimated 38% of the time. X-ray evaluation of insertion depth confirmed that the second portion of the duodenum was reached in 96%, third portion in 51%, and fourth portion or beyond in 38% of patients. We conclude that fluoroscopic confirmation may be necessary when endoscopically assessing distal duodenal segments for pathology.