A self-expanding prosthesis delivery system comprising: an outer tubular structure having a proximal end portion and a distal end portion, said distal end portion configured to receive a self expanding prosthesis; an inner tubular member adapted for tracking over a guidewire, having a proximal end portion fixed to a handle and a distal end portion fixed to a first sealing member , and being disposed in said outer tubular structure ; at least a portion of said outer tubular structure being movable relative to said inner tubular member such that at least a portion of said outer tubular structure can be retracted, while at least a portion of said inner tubular member is held in a fixed position relative to said outer tubing structure ; said outer tubular structure and inner tubular member being radially spaced from one another so as to form a fluid fillable space having first and second ends; wherein said first sealing member is fixedly secured to said inner tubular member at a location proximal to said distal end portion to fluidly seal said first end of said fluid fillable space , said first sealing member extending from said inner tubular member to said outer tubular structure and being in sealing engagement with said outer tubular structure , and a second seal arranged at said second end of said fluid fillable space formed by said handle to fluidly seal the second end of said fluid fillable space , wherein said outer tubular structure , inner tubular member , first sealing member , and said second seal form a chamber , which has a constant volume that remains constant when said moveable portion of said outer tubular structure is retracted relative to said inner tubular member . an outer tubular structure having a proximal end portion and a distal end portion, said distal end portion configured to receive a self expanding prosthesis; an inner tubular member adapted for tracking over a guidewire, having a proximal end portion fixed to a handle and a distal end portion fixed to a first sealing member , and being disposed in said outer tubular structure ; at least a portion of said outer tubular structure being movable relative to said inner tubular member such that at least a portion of said outer tubular structure can be retracted, while at least a portion of said inner tubular member is held in a fixed position relative to said outer tubing structure ; said outer tubular structure and inner tubular member being radially spaced from one another so as to form a fluid fillable space having first and second ends; wherein said first sealing member is fixedly secured to said inner tubular member at a location proximal to said distal end portion to fluidly seal said first end of said fluid fillable space , said first sealing member extending from said inner tubular member to said outer tubular structure and being in sealing engagement with said outer tubular structure , and a second seal arranged at said second end of said fluid fillable space formed by said handle to fluidly seal the second end of said fluid fillable space , wherein said outer tubular structure , inner tubular member , first sealing member , and said second seal form a chamber , which has a constant volume that remains constant when said moveable portion of said outer tubular structure is retracted relative to said inner tubular member . <EOS>