Serial abdominal ultrasonography was performed in 37 children being treated with ceftriaxone for serious infections. Biliary concrements developed in 16 patients, causing symptoms in 3, one of whom also had urolithiasis with renal colic and obstructive ureteropyelectasia. After cessation of ceftriaxone treatment, ultrasound abnormalities and symptoms gradually disappeared, with complete sonographic resolution after 2 to 63 days.