We report a pudendal nerve injury that developed after a posterior approach to the sciatic nerve. A classical Labat's posterior sciatic nerve block on the right side was performed using an insulated needle and a nerve stimulator set at an initial current of 2 mA, 2 Hz frequency, and 0.1 ms duration. Painful paresthesia radiating to the right side of the patient's penis and right leg was experienced shortly after needle insertion. The needle was immediately withdrawn and redirected laterally. Motor responses for the common peroneal and tibial components of the sciatic nerve were elicited at 0.48 mA in both cases and a 10-mL bolus of mepivacaine 1.5% was injected onto each component. The sciatic nerve block was combined with a femoral nerve block to facilitate a knee arthroscopy. The trauma resulted in erectile dysfunction and partial loss of penile sensation as well as evidence of injury to the sciatic nerve itself. Symptoms and clinical signs of pudendal nerve injury lasted 7 months. This is the first time that sexual dysfunction as a result of a unilateral pudendal nerve injury that occurred after a posterior sciatic nerve block has been reported.