To assess the potential role of magnetic resonance (MR) imaging in the follow-up evaluation of small hepatocellular carcinoma (HCC) treated with percutaneous ethanol injection (PEI), 31 patients with a single HCC lesion less than 3.0 cm in diameter underwent MR imaging at 0.5 T before and after treatment. Posttreatment follow-up included contrast material-enhanced computed tomography (CT) and fine-needle biopsy in all cases. The most important characteristic of the treated HCC lesions was hypointensity on T2-weighted MR images in cases (27 of 31) in which complete tumor necrosis was achieved with PEI. This feature corresponded to a nonenhanced, low-attenuation area on follow-up contrast-enhanced CT scans. Four HCCs were positive for malignant cells at 6-month fine-needle biopsy; in these lesions, residual tumor tissue was of high signal intensity on T2-weighted MR images and of high attenuation on contrast-enhanced CT scans. In each case, incomplete tumor necrosis was confirmed at pathologic examination of the surgical specimen.