We report a rare case of robot-assisted laparoscopic radical prostatectomy (RARP) in a patient with a preexisting penile prosthesis. In this case, we completed RARP without removing the reservoir by using a deflation-inflation technique, and there were no complications related to the prosthesis. The patient had a negative surgical margin. The preserved three-piece inflatable penile prosthesis continued to function properly in 1 month. Reservoir-preserving RARP is technically feasible and safe. However, it is important to be aware of device-related complications. Long-term studies on the mechanical survival rate and patient satisfaction should be also performed