Sonography provided an accurate diagnosis in 10 preoperative studies and correctly showed the extent of the lesions in two postoperative examinations in a group of 12 children with surgically proven intraabdominal lymphangiomas. These masses typically contained anechoic fluid in one or more contiguous cystic loculations bounded by or containing one or more 1- to 2-mm thick septa. Thicker septa occurred in several cases with inflammation and/or accumulations of fatty tissue. Chylous or creamy fluid displayed fine diffuse echoes, whereas hemorrhage resulted in coarse echoes and/or solid masses. In two patients unusual renal involvement mimicked polycystic kidney disease. Typical sonographic appearances of lymphangioma may be radically altered by hemorrhage, inflammation, and unusual sites of involvement.