A pigmented fundus lesion in a 47-year-old woman gave a positive 32P test result and angiography showed a separate tumor circulation suggesting a diagnosis of choroidal melanoma. Examination after local resection of the tumor revealed massive retinal gliosis, a rare condition not normally considered in the differential diagnosis of choroidal melanoma. We review the clincial and histologic features that differentiate massive retinal gliosis from choroidal melanoma and astrocytic hamartoma.