A sterile implantable device intended to extend the cylinder component of a penile prosthesis to achieve an overall cylinder length which fits the measurements of the patient's anatomy (i.e., corpora cavernosa length). It is a synthetic polymer (e.g., silicone) moulded cap available in a variety of sizes and is intended to be attached to the end of a penile prosthesis cylinder during implantation, in cases where the cylinder is of insufficient length.