A locking adjustment turret for rifle scopes includes a stationary portion mounted on an outer tube of the scope, a rotating adjustment portion supported in the stationary portion and including an adjustment knob such that rotation of the knob results in axial motion of a shaft toward and away from an inner tube of the scope, and a locking mechanism on the rotating adjustment portion that locks the shaft in a desired position. The locking mechanism includes a pin that engages a detent mechanism in the rotating adjustment portion, preventing rotation of the rotating adjustment portion. The locking mechanism is operated with a lock knob that sits atop the adjustment knob and is accommodated by a recess in the top of the adjustment knob.