The diagnostic significance of several radiopharmaceuticals for malignant uveal melanoma has been discussed in the past decade. In our study, 99 patients with clinically suspected malignant uveal melanoma were considered; 36 had been treated and 63 were untreated. Single-photon emission computed tomography (SPECT) images were obtained after the intravenous injection of N-isopropyl- p-[(123)I]iodoamphetamine ((123)I-IMP). In the 63 patients without prior treatment, 36 were negative on (123)I-IMP SPECT, and all 36 except for 1, were histologically or clinically confirmed as having other, benign, entities including choroidal nevus, choroidal hemangioma, metastatic choroidal tumor, and other intraocular conditions. Twenty-seven of the 63 patients showed significantly high accumulation of (123)I-IMP in the late phase in the area corresponding to the intraocular lesion; all except 2 of these 27 patients were histopathologically or clinically confirmed as having malignant uveal melanoma. One of these 2 (123)I-IMP-positive patients was histologically diagnosed with adenocarcinoma arising from the pigment epithelium of the ciliary body. The 36 patients who had undergone eye-preserving treatments such as brachytherapy showed various results on (123)I-IMP SPECT. We concluded that (123)I-IMP SPECT is useful for the diagnosis of malignant uveal melanoma, especially in patients with atypical clinical manifestations for which conventional diagnostic techniques are inadequate to arrive at a definitive diagnosis.