Endoscopy is a safe technique with a sensitivity and specificity superior to those of conventional diagnostic procedures, which it has consequently replaced. In doing so, it has also altered many diagnostic and therapeutic concepts. Moreover, endoscopy has positively influenced the previously unaffected course of certain diseases, e.g. upper G. I. bleeding. Endoscopy benefits both the patient and the physician. Although no complete cost-benefit analysis is available, preliminary reports have been favourable. These aspects indicate that endoscopy is highly valuable in a clinical setting. It must be pointed out, however, that endoscopy as a whole has not yet been fully analyzed in any single given clinical study.