Purpose: The effectiveness of 10 mL and 20 mL local prilocaine infiltration for analgesic purposes during shockwave lithotripsy (SWL) was compared, and the differences in pain intensity and need for additional analgesics were defined. Patients and Methods: One hundred and twenty-one patients between the ages of 16 and 69 with kidney stones were randomly separated into two groups. The 60 patients in group 1 received 10 mL prilocaine subcutaneously and deep lumbar infiltration into the area 1 cm below the twelfth rib 2 minutes before SWL. The 61 patients in group 2 received 20 mL subcutaneously and deep lumbar infiltration of prilocaine to the same locale, again 2 minutes before the process. All the patients received one session of SWL. For measurement of pain intensity, the 0 to 100 mm visual analog scale (VAS) was used at 1 minute and every 10 minutes during the process. Intravenous fentanyl was administered to patients who had steady or increasing intensity of pain during the process. Results: VAS values were statistically significantly higher in patients in group 1 compared with patients in group 2 during the process. While 40 patients received additional analgesia in group 1, only three patients in group 2 needed additional analgesia. Conclusion: Use of 20 mL subcutaneous and deep lumbar prilocaine infiltration during SWL for analgesic purposes is recommended as an efficient, cost-effective, anesthetist-independent, and reliable method. © Mary Ann Liebert, Inc. 2008.