ObjectiveTo determine whether a difference in the behavioral and physiologic response to circumcision can be demonstrated between neonates undergoing the procedure with ring block and those receiving no anesthesia.MethodsForty healthy male newborns were assigned randomly to receive either ring block or no anesthesia. Indices of perceived pain including crying time, behavioral state, oxygen saturation, and heart and respiratory rates were recorded at baseline and at intervals during the circumcision. Infants were reassessed 2 minutes and 2 hours postoperatively.ResultsInfants receiving ring block cried less than did controls (P< .001). Anesthetized infants had smaller increases in heart rate (P< .005) and demonstrated less arousal (P< .005) during each operative interval. For all operative intervals combined, anesthetized infants had a smaller decrease in oxygen saturation (P< .001) and a smaller increase in respiratory rate (P= .005) than did controls. Two minutes postoperatively, anesthetized infants had returned to their baseline behavioral state, whereas controls remained significantly more aroused (P< .005). Two hours postoperatively, there were no significant differences in any variables between the groups, nor between each group and its baseline. There were no complications related to anesthesia administration.ConclusionNeonatal circumcision causes behavioral and physiologic changes consistent with the perception of pain. Ring block is an effective method of anesthesia for this procedure.