To evaluate the detectability of hepatocellular carcinoma (HCC) at artery-dominant phase and to compare it with that at precontrast and delayed-contrast phases, 34 patients with 109 HCCs were examined by ultrafast computed tomography (CT) using an incremental dynamic technique under single breath-holding. Images of three phases (precontrast, artery-dominant, and delayed) were compared with iodized-oil CT images. None of the lesions were detected only at precontrast phase. HCC detectability at the artery-dominant phase (87/109, 80%) was significantly superior to that at precontrast phase (32/109, 29%) (p < .01) and delayed-contrast phase (57/109, 52%) (p < .01). All 31 lesions missed at delayed-contrast phase were depicted at artery-dominant phase, while one lesion observed at delayed-contrast phase was missed at artery-dominant phase. Incremental dynamic CT at artery-dominant phase was suitable for the diagnosis of HCCs. Precontrast phase images were not necessary, although delayed-phase images were useful for the evaluation of tumor extension in some cases.