The present invention relates to a mounting adapter for releasably securing accessories, tools, or their medical instruments to the distal end of an endoscope. The adapter is compatible with endoscopic accessories that have a cylindrical mounting surface, which becomes positioned over a length of the distal end of an endoscope. The adaptor is preferably provided in two components to support both ends of a cylindrical accessory on the endoscope surface. The adapter is configured to hold the accessory on the endoscope shaft by frictional engagement and is configured to maintain the accessory concentric with the shaft along its length. The adapter also is configured to mount an accessory to a wide range of commercially available endoscope diameters.