The efficacy of various imaging procedures used for the diagnosis of small hepatocellular carcinomas (HCCs) (lesions no larger than 3 cm in diameter) was evaluated in a retrospective study of 100 patients. Seven patients with hepatic adenomatous hyperplastic nodules containing HCC foci were also assessed. In 89 patients, the lesion was initially detected during follow-up of chronic liver disease. In 21 patients, it was first diagnosed on the basis of elevated serum alpha-fetoprotein; in the remaining 79 it was diagnosed incidentally with imaging procedures. The overall sensitivities of sonography (84%), CT (84%), and angiography (81%) were compared with those of arterial angiographic CT (82%), portal angiographic CT (91%), lipiodol CT (93%), and intraoperative sonography (96%). The differences in sensitivity between angiography and lipiodol CT (p less than .05) and between intraoperative sonography and the other studies (p less than .01) were statistically significant. In 22 lesions smaller than 1 cm, the sensitivities of lipiodol CT and intraoperative sonography were high (83% and 86%, respectively). Adenomatous hyperplasias containing HCC foci were frequently detected by arterial angiographic CT and intraoperative sonography. These results show that sonography or CT and alpha-fetoprotein are useful in detecting small HCCs in screening programs of patients with chronic liver disease. Lipiodol CT and intraoperative sonography are necessary in patients who are candidates for surgery.