A disposable outer bladder prosthesis is described, said prosthesis comprising a bag having an inner face, an outer face, an upper portion and a lower portion, wherein said upper portion comprises an opening configured to allow the passage through it of the genitals (penis and scrotum) of a male user and an edge configured to close, at least in part, said opening around said genitals and wherein said lower portion comprises a reservoir for containing the user's urine. The edge of the opening may be elastic and provided with double-sided adhesive tape or the like.