Complications of Zenker's diverticulum are rare and include ulcer, bleeding and malignancy. Ulcer in the basis of diverticulum is a very rare complication and to date only four cases have been reported in the literature. Herein, we report a new case of ulcer in Zenker's diverticulum mimicking esophageal malignancy presumed to be due to aspirin and/or alcohol consumption. The exact diagnosis was troublesome and needed to perform diagnostic procedures repeatedly. The patient underwent external pharyngoesophageal diverticulectomy. We emphasize that endoscope should be withdrawn if any resistance is encountered during esophageal intubation-even with forward-viewing endoscope-especially when there is a Zenker's diverticulum suspicion and the patient receives ulcerogenic agents. Endoscopic examination should be performed prior to any definitive surgical procedure in all patients with Zenker's diverticulum.