Report on an extremely rare case of primary bilateral malignant melanoma of the choroid with histological verification of both tumors. The patient was a 54-year-old woman; the presumptive clinical diagnosis was a primary bilateral melanoblastoma. A thorough general examination did not reveal any metastases. Six months later the patient underwent surgery. The left eye, in which the tumor was larger, was enucleated and a B-type malignant melanoma of the choroid with invasion of the sclera was diagnosed histologically. Two months later the patient died of a lung embolism. Histological verification of the tumor of the right eye led to the same diagnosis as in the left eye, but without invasion of neighbouring structures. No distant metastases were found at autopsy. A thin layer of slender spindle nevus cells was found between the tumor and the sclera during the histological study. The author agrees with Yanoff and Zimmerman (1967) that this may be regarded as the origin of the malignant tumor.