PURPOSE: The purpose of this study was to evaluate sonographic findings of ceftriaxone-associated pseudolithiasis in gallbladder(GB). MATERIALS AND METHODS: Fifty-seven children who received ceftriaxone treatment were prospectively evaluated with ultrasound(US). Serial US examinations were performed at 1st-3rd day and at 5th-9th day after the initia-tion of ceftriaxone treatment in all patients. In eight of the patients with pseudolithiasis on 5th-9th day examina-tions, follow-up studies were also performed every 5-7 days until the pseudolithiasis had completely resolved. The incidence and type of pseudolithiasis and posterior acoustic shadowing associated with pseudolithiasis were analyzed. The types of pseudolithiasis were classified as floating dots, linear, globular, and combined. RESULTS: GB pseudolithiasis was found in 17(30%) of 57 patients. According to the types of pseudolithiasis, there were four floating dots, four linear, one globular, and eight combined types. Posterior acoustic shadowing was present in 13(76%) of 17 patients. All pseudolithiasis was demonstrated on 1st-3rd day examinations and com-pletely resolved within 15 days after the stopping of ceftriaxone treatment in all of the patients in whom follow-up studies were available(mean = 9.2 days). CONCLUSION: GB pseudolithiasis can be associated with ceftriaxone treatment and it can mimic a stone. When a GB stone is demonstrated on US in a pediatric patient, the possibility of ceftriaxone-associated pseudolithiasis should be considered for accurate diagnosis and appropriate treatment.