A trans-endoscopic hydraulic balloon dilation apparatus includes a fluid reservoir containing a hydraulic fluid. A shaft has a lumen in fluid communication with a leading end of the fluid reservoir. A balloon is mounted on the shaft and an opening in the shaft enables hydraulic fluid to flow through the opening into or from the balloon. A piston secured to a leading end of a piston rod is slideably positioned within a lumen of the fluid reservoir. A hub secured to a trailing end of the fluid reservoir is centrally apertured to accommodate the piston rod so that a trailing end of the piston rod is external to the fluid reservoir. Displacement of the piston rod in a trailing-to-leading direction causes expansion of the balloon. Displacement of the piston rod in a leading-to-trailing direction causes deflation of the balloon. The piston can be locked into any position.