In a prospective study, the relationship between the clinical severity of dengue haemorrhagic fever (DHF) and the sonographic findings was examined. The study comprised 73 cases classified as mild (grades I–II) and 75 as severe (grades III–IV). Ultrasonography in the mild group revealed pleural effusions in 30 %, ascites in 34 %, gallbladder wall thickening in 32 %, hepatomegaly in 49 %, splenomegaly in 16 %, and pancreatic enlargement in 14 %. In the severe group, pleural effusions, ascites and gallbladder wall thickening were found in 95 %, pararenal and perirenal fluid collections in 77 %, hepatic and splenic subcapsular fluid collections in 9 %, pericardial effusion in 8 %, hepatomegaly in 56 %, splenomegaly in 16 %, and pancreatic gland enlargement in 44 %. Ultrasound may be useful for early prediction of the severity of DHF in children.