OBJECTIVE. We performed color Doppler imaging of the right lower quadrant in children with acute appendicitis to characterize the imaging findings indicative of appendiceal perforation and to determine the value of this technique in diagnosing appendiceal abscesses. SUBJECTS AND METHODS. Forty- seven children with surgically proven appendicitis underwent color Doppler sonography of the right lower quadrant as an adjunct to gray-scale sonography. At pathologic examination, 27 patients had nonperforating appendicitis and 20 patients had perforating appendicitis. In the latter group, seven patients had abscesses and 10 had phlegmon. The color Doppler sonograms were evaluated for the presence or absence of appendiceal hyperemia, hyperemic periappendiceal or pelvic fluid collections, and hyperemic soft tissues in the right lower quadrant. RESULTS. Color Doppler sonography showed appendiceal hyperemia in 21 (78%) of the 27 patients with nonperforating appendicitis and in eight (40%) of the 20 patients with perforating appendicitis. The hyperemia was scattered in 14 (67%) of the 21 patients without perforation and in six (75%) of the eight patients with perforation. The remaining patients with blood flow identifiable on color Doppler sonography had focal appendiceal hyperemia. For seven (35%) of the 20 patients with perforating appendicitis, color Doppler examination showed hyperemic, loculated periappendiceal or pelvic fluid collections, subsequently proved to be abscesses at surgery. No patient with nonperforating appendicitis had a hyperemic, loculated periappendiceal or pelvic fluid collection. Ten patients with perforating appendicitis displayed increased color Doppler signal in the adjacent right-lower-quadrant bowel loops and soft tissues, indicating phlegmon or peritonitis. CONCLUSION. Our results indicate that the best color Doppler sonographic predictors of appendiceal perforation are a hyperemic periappendiceal or pelvic fluid collection and periappendiceal soft-tissue hyperemia. A hyperemic, loculated fluid collection appears specific for the diagnosis of abscess.