Abstract: An implantable double walled tissue augmentation prosthesis consisting of a gel or liquid filled container within a liquid fillable container. A one-way flap valve is positioned within the wall of the liquid fillable container so that liquid may be selectively added to that container for inflation. Following implanting of the prosthesis, the liquid filled container may be deflated by removal of liquid therefrom to reduce any spherical contracture of the prosthesis caused by tissue contraction around the prosthesis. The prosthesis is most suitable for mammary augmentation.