The authors report a case of a primary melanoma of the esophagus, which is a rare neoplasm with poor prognosis. The diagnosis of malignant melanoma was suggested, on endoscopic biopsies, because of the presence of large malignant cells with abundant cytoplasm containing melanin pigment positive in the Fontana-Masson's reaction. These cells were immunoreactive for S100 protein while they did not show staining for antiepithelial membrane antigen and anti-keratin antibodies. Moreover ultrastructural study of the tumor cells revealed cytoplasmic aberrant premelanosomas. An important histological feature of the present case, which confirmed the primary oesophageal nature of the tumor was the presence of foci of melanosis (benign melanocytes) within the oesophageal epithelium which was adjacent to the melanoma. The variation in the histology of malignant melanoma may provide difficulties in diagnosis especially if one is limited to study a small biopsy specimen. In such cases other diagnoses including epidermoid carcinoma with prominent spindle-cell features and sarcomas should be eliminated by means of immunohistochemical and ultrastructural studies. The particular feature of our case, which apparently has not been reported previously, is the identification of the melanosis two years prior to the diagnosis of the malignant melanoma. The present study indicates that the identification of this lesion is of important diagnostic interest and might lead to the follow-up surveillance of the melanosis by multiple biopsies.