Magnetic resonance imaging (MRI) was performed on 13 patients with choroidal tumors to determine whether this technique could detect and portray an intraocular tumor and to investigate additional biochemical parameters of the diseased tissue. In 11 of 13 patients, the lesion was depicted, and its gross morphology was outlined with a clarity approaching that of computed tomography. We were able to apply principles derived from MRI studies in other portions of the body and identify trends in the characterization of lesions of different etiologies. The relative T1 and T2 values for each of the major pathologic categories (malignant melanoma, metastatic carcinoma, and benign choroidal lesions) are presented and discussed. In addition, MRI was clearly superior to other techniques in the detection and delineation of associated intracranial lesions.