Abdominal CT was the primary diagnostic method used to evaluate 40 patients with suspected periappendiceal abscess. Its subsequent impact on patient management was then analyzed for several categories of clinical presentation, including patients with and without a palpable right-lower-quadrant mass and postoperative patients. CT was reliable in distinguishing periappendiceal abscesses from phlegmons; 17 of 18 patients with phlegmons responded promptly to antibiotic therapy alone without need for surgery. Patients with larger, poorly localized abscesses underwent early surgical drainage. CT was successful in guiding percutaneous catheter drainage (nine patients) or aspiration (one patient) of well-localized periappendiceal abscesses in 10 of 11 patients. One attempted catheter drainage guided by sonography was technically unsuccessful. In patients without a palpable right-lower-quadrant mass, CT was helpful in establishing the diagnosis of periappendiceal inflammation. However, there were three false-positive diagnoses in patients with pericecal fluid collections including a ruptured cecal lymphoma, a ruptured cecal diverticulum, and a ruptured corpus luteum cyst. A diagnostic approach with CT is presented in patients with suspected periappendiceal abscess.