Magnetic resonance imaging (MRI) and computed tomography (CT) were performed in four patients with thorotrastosis. On CT scan, Thorotrast (thorium oxide) deposition was shown as high-density areas in the liver and spleen and the abdominal lymph nodes. These deposits were not found on MRIs. Splenic volume was significantly small due to atrophy. The contrast-noise ratio in the spleen on T1-weighted images was significantly lower. Thorotrast deposition does not affect MRI appearance; therefore it may be useful for the early detection of malignant tumors as a complication of thorotrastosis.