To assess the efficacy of transversus abdominis plane (TAP) block as anesthesia method for retroperitoneal varicocele repair and to evaluate its postoperative analgesic effectiveness. Thirty-three consecutive male patients undergoing retroperitoneal varicocele repair (Palomo technique) were enrolled in this study. Patients were randomly allocated to undergo ultrasound-guided TAP block anesthesia (case group), or conventional spinal anesthesia (control group). The primary outcome was the evaluation of the proportion of patients achieving an adequate anaesthesia (as evaluated by prinprick sensation test and by the need of analgosedation). We have also evaluated pain during the intervention and pain on movement, pain at rest, rescue analgesia need, nausea, and satisfaction at different time-points (6, 12, and 24 h after surgery). The proportion of patients achieving adequate anesthesia was not different between the groups (p = 0.1). In the post-operative evaluation, patients enrolled in the case group expressed significantly less pain on VAS score at rest and on movement at 6 (p = 0.001 and p = 0.001) and at 12 h (p = 0.004 and p = 0.01). Moreover, the need of rescue analgesia resulted significantly higher in the control group (p = 0.03). This is the first study showing that TAP block could be employed as an effective and feasible anesthesia method for the retroperitoneal varicocelectomy. Moreover, our results demonstrate that this method is more effective than spinal anesthesia in the pain control after varicocele repair.