Ultrasonically (US) guided fine-needle aspiration biopsy was performed in 88 patients who had gallbladder masses. All masses were less than 4.8 cm in diameter. A 22- or 23-gauge, Teflon-coated needle was placed into the mass with the transhepatic or transperitoneal route. By means of this technique, gallbladder malignancy was confirmed in 69 of the 78 cases of malignancy (88.5%). Ten of 10 benign lesions were properly categorized. One patient developed bile peritonitis following a single needle pass with the transperitoneal approach. Pain, a minor complication of the procedure, was noted in four cases. No instances of hemorrhage or vasovagal reactions occurred. From their experience in this large series, the authors conclude that US-guided fine-needle aspiration biopsy of gallbladder masses is a safe, reliable, and accurate technique for the diagnosis of malignancy.