We report the case of a 3-month-old boy with a right-sided sliding appendiceal inguinal hernia that was diagnosed preoperatively with sonography. Surgery was performed, and intraoperative and histopathologic evaluations also revealed changes in the appendix that could have led to complications if left untreated. The infant's recovery was uneventful, and he was discharged on the second day after surgery. This condition is usually diagnosed intraoperatively, and to the best of our knowledge, this is only the second report in the English-language medical literature in which such a case was correctly diagnosed preoperatively with sonography. In our case, the early sonographic diagnosis led to early intervention and the avoidance of potential complications. (C) 2003 Wiley Periodicals, Inc.