OBJECTIVE The purpose of this study was to determine the following: whether the arterial supply of a normal appendix is visible with Doppler sonography; whether the physiologic vasodilatation that accompanies childhood appendicitis is visible; what Doppler patterns appear once necrosis of the appendix has occurred; what Doppler shifts are visible with chronic, recurrent appendicitis; and whether other conditions in the right lower quadrant can mimic the Doppler sonographic patterns of appendicitis. METHODS Twenty-five fasting patients without abdominal pain or intestinal disease and 45 patients (1-25 years old; mean, 8 years old) with right lower quadrant pain and suspected appendicitis were examined sonographically, using 5- and 7-MHz linear, color, and pulsed Doppler transducers. Arterial signals were sought within the appendix and neighboring tissues, counted, and classified as sparse (1-2), moderate (3-4), or abundant (>4). The resistive index (RI) was measured. Thirty patients who underwent surgery were retained for surgical and pathologic correlation, and only they formed the appendicitis study. RESULTS A normal appendix was found in 10 patients. Doppler shifts were sparse, and diastolic flow was low or absent (RI, 0.85-1). Acute uncomplicated appendicitis was found in 13 patients, who had abundant color Doppler signals throughout most of the appendix, with high diastolic flow (RI, 0.40-0.77; mean, 0.54). Acute necrotic appendicitis with perforation was found in 11 children, eight of whom showed no signals in the necrotic area at the tip. Few or no signals were seen in the remainder of the appendix (RI, 0.33-0.90; mean, 0.54). In two patients, signals were abundant in the tissues surrounding the appendix. Recurrent or chronic appendicitis was found in three patients, previously diagnosed as having Crohn's disease, psychosomatic illness, or nonspecific abdominal pain. The appendix had Doppler signals confined to the tip (RI, 0.63-0.83; mean, 0.75). Other diagnoses were found in three patients, in whom the appendix was not seen. There were abundant color signals in the intestinal wall and adjacent tissues in the right lower quadrant. Two patients had Crohn's disease, and the third had an unsuspected early pregnancy. The appendix was normal in all. CONCLUSIONS Acute appendicitis is accompanied by inflammatory hypervascularity reflected as an increased number of color signals and higher diastolic Doppler shifts as compared with those found in normal persons. No Doppler shifts are identified in areas of appendiceal ischemia. Other acute inflammation in the right lower quadrant also produces numerous Doppler shifts with high diastolic flow, as does ovulation. Care must be taken to identify the source of these Doppler signals. The changing vascularity of healing, recurrent, and chronic appendicitis promises to further our understanding of the pathogenesis and evolution of this disease.