A prophylactic ankle brace for protecting the ankle of paratroopers and which fits on the outside of the paratrooper boot. It includes lateral and medial side walls extending longitudinally upwardly to encompass the ankle and lower extremity of the leg above the ankle with a substantially U-shaped member connecting the spaced apart side walls for extending substantially around and conforming to the back of the shoe to hold the side walls in fixed relationship to each other and to the shoe. Straps are provided for removably attaching the connected side walls to the shoe and to the lower extremities of the leg in fixed relationship.