99mTc-HIDA cholescintigraphy was performed in 6 patients with Dubin-Johnson syndrome and 1 patient with Rotor syndrome. In the patients with Dubin-Johnson syndrome, the cholescintigrams had a characteristic pattern of delayed visualization or nonvisualization of the gallbladder and bile ducts in the presence of intense, homogeneous, and prolonged visualization of the liver. In the patient with Rotor syndrome, the hepatobiliary system was not visualized at all. It is concluded that 99mTc-HIDA cholescintigraphy may be helpful in the diagnosis of Dubin-Johnson syndrome and Rotor syndrome and in the differential diagnosis between these two conditions.