Within a 3 year period from July 1996 to July 1999, a total of 105 children with clinical diagnosis of cellulitis were evaluated by ultrasonography. Eighty-six children (age range, 17 days to 15 years) fulfilling the sonographic criteria for diagnosis of cellulitis were enrolled into the study. The sonographic features were used to correlate with clinical symptoms and their duration, the peripheral leukocyte count, and the serum C-reactive protein level. Pus aspiration for immediate microscopic and later bacteriologic studies was carried out under sonographic guidance. Ultrasonographic features of cellulitis included subcutaneous tissue thickening without distortion and pus (25 cases, 29%), distortion of subcutaneous tissue without pus accumulation (26 cases, 30%), distortion of subcutaneous tissue with pus accumulation (19 cases, 23%), and distortion of tissue with abscess formation (16 cases, 18%). The presence of sonographic features of tissue distortion with or without pus accumulation, including abscess formation in children with cellulitis, correlated with a longer duration of symptoms (greater than 4 days), the presence of high-grade fever, higher peripheral leukocyte count, and higher serum C-reactive protein levels. Those patients who underwent sonographically guided aspiration or surgical intervention showed a shorter hospital stay and fever duration than those without such aspiration. Our results indicated that ultrasonography is of great value in managing cellulitis by providing information regarding the progression of inflammation. Sonographically guided aspiration of pus may be a treatment of choice, as it may decrease the need for operation.