A penis erection stimulation system comprises one or more infusion needles disposed within and implanted along with one or more housings adjacent the patient's left and right corpora cavernosa. A reservoir and a pump are also implanted inside the patient's body to supply the infusion needle with infusion liquid. A drive unit also adapted for implantation inside the patient's body is arranged for advancing and retracting the tip end of the infusion needle such that it penetrates the housing in at least one penetration area, preferably at least in two different penetration areas either simultaneously or in immediate time succession, thereby injecting drugs along with the infusion liquid into the patient's body for stimulating penis erection. The outer wall of the housing accommodating the infusion needle comprises at least one door in the penetration area or areas. A drive is connected to the door for actively opening the door so as to allow for the infusion needle to be advanced through the opened door. The door may comprise a flap, such as a resilient, normally closed flap. It is particularly preferred if the drive connected to the door forms part of the drive unit coupled to the infusion needle. More specifically, the arrangement may be such that advancement of the infusion needle by means of the drive unit simultaneously causes the drive to open the door.