Much discussion in the literature concerning Zenker's diverticulum is related to etiology. Various theories have been propounded, but no single conclusion is generally accepted. We believe that an anatomic predisposition plays a prominent role. Considerations for this conclusion will be discussed. In the otorhinolaryngology departments of University Hospital and Martini Hospital (Groningen, the Netherlands) 545 patients with a diverticulum were treated endoscopically since 1964. Initially we used the procedure described by Dohlman. With the increase in the number of patients, the technique and instruments used have improved. In 1981 we started to apply a microendoscopic procedure with a special double-lipped scope and the carbon dioxide laser. The rate of complications was very low, and 91% of the patients are highly satisfied. In view of our results, we feel justified in maintaining that endoscopic treatment is a relatively safe and effective method.