This study attempts to investigate whether gallbladder wall thickening (GBWT) measured by ultrasonography can be used in children as a reliable criterion to predict the onset of severe dengue hemorrhage fever (DHF). In this prospective study, we performed ultrasound examinations focusing on the gallbladder wall and the presence of intraperitoneal free fluid in 48 mild DHF cases (grades 1-11) and 48 severe cases (grades 111-IV). GBWT varied between 1 mm and 8 mm with a mean of 3.77 mm & 2.04 mm. The mean value of DHF grades I and I1 (2.39 mm 5 1.48 mm) is significantly lower than that of grades I11 and IV (5.14 mm & 1.54 mm), p < 0.001. GBWT exceeded 3 mm in only 16 of 48 (33.3%) grade 1-11 patients and in 45 of 48 (93.8%) grade 111-IV patients. A significant positive correlation was apparent between GBWT and the severity of illness, p < 0.001. Patients with ascites have significantly thicker gallbladder walls than those without, p < 0.01. In clinically confirmed DHF cases, the sonographic finding of GBWT >3 mm to 5 mm, with 93.8% sensitivity, can be used as a criterion indicating the need for admission and monitoring. A GBWT of 2 5 mm, with 91.7% specificity, is useful as a criterion for identifying DHF patients at high risk of developing hypovolemic shock.