Retrospective and prospective studies were performed to investigate the ultrasonic findings of diffuse-type cholesterosis of the gallbladder. In retrospective studies performed in 4 cases, ultrasonic images of a resected gallbladder created by the water immersion method showed the three-layer structure of the wall; hyperechoic spots arranged with the dotted-line appearance on the inner surface, a narrow hypoechoic band lying almost directly below that, and a hyperechoic layer on the outer surface. Comparative studies with histological findings of the specimen indicated that the echogenic origin of each structure was, in turn, granular excrescences filled with foamy cells, a muscular layer and subserosal tissue, and serosa. Such a three-layer structure had been imaged on preoperative ultrasonograms in 2 of 4 cases. Prospective studies were carried out by using the finding of the dotted-line appearance with a hypoechoic band as the principal ultrasonic image of diffuse-type cholesterosis of the gallbladder. A preoperative diagnosis of the disease was carried out in 7 of 8 operative cases. The water immersion ultrasonography of the resected gallbladder revealed the principal ultrasonic image of the disease. In 43 nonoperative cases of the disease, the finding that hyperechoic spots are floating and moving in the gallbladder by extracorporeal vibration (dancing sign) was observed in 5 cases (11.6%), while the comet-like echo was found in 4 cases (9.3%). The coexistence of these findings may further strengthen the diagnose of the disease. In conclusion, the dotted-line appearance with a hypoechoic band is the principal ultrasonic finding, and is characteristic of diffuse-type cholesterosis of the gallbladder.