PURPOSE: To evaluate power Doppler ultrasonograhic findings of the enlarged mesenteric lymph nodes, and to compare between patients with and without acute abdominal pain. MATERIALS AND METHODS: Thirty-seven children with acute abdominal pain and thirty-three asymptomatic children all with the enlarged mesenteric lymph nodes in whom power Doppler ultrasonography was performed were included in this study. The enlarged lymph nodes were evaluated for number, size, shape (ratio of long to short axis diameter: L/S ratio), distribution and hilar vascularity on gray scale ultrasonography while the flow pattern (3 types: nonvascular, hilar, peripheral type) of the vascularity was analyzed with power Doppler ultrasonography. The hilar pattern of vascular flow type was graded into I to III depending upon color signal. The comparison between symptomatic group and asymptomatic control group was analyzed with gray scale ultrasonography and power Doppler ultrasonography. RESULTS: The number of enlarged lymph nodes (n>or=10) was greater in the symptomatic group (29/37, 78%) than in the control group (6/33, 18%) (p<0.01). The mean size of the largest lymph node between two groups was different with a statistical significance; the mean long diameter was 12.4+/-3.1 mm (short diameter 5.8+/-1.6 mm) in the symptomatic group and 11.1+/-2.3 mm (4.5+/-1.3 mm) in the control group (p<0.05). The mean L/S ratio of the largest one was 2.2+/-0.6 in the symptomatic group and 2.7+/-0.8 in the control group (p<0.05). Lymph nodes were detected in both right lower quadrant of the abdomen and periumblical region in 16 (43%) of the symptomatic group and 3 (9%) of the control group (p<0.01). On power Doppler ultrasonography, hilar type of vascularity was noted in 22 (67%) cases of the control group and all of symptomatic group. The prevalence of exuberant hilar flows (grade II / III) in the symptomatic group (28/37, 76%) was significantly higher than that of the control group (4/33, 12%) (p<0.01). CONCLUSION: Enlarged mesenteric lymph nodes in the symptomatic group with acute abdominal pain tend to be larger, spherical or ovoid with exuberant hilar pattern of blood flows when compared with those of the asymptomatic control group.