The difficulty of differentiating an epithelial skin tumour with partial adenoid histological features from a metastasis of an internal adenocarcinoma is exemplified by a case report of an 83-year-old woman. Histological, histochemical and ultrastructural results led us to suppose that two different carcinomas with metastases were present: an adenocarcinoma of the colon and a ‘unicellular muciparous squamous cell carcinoma of the skin’. The nosological proximity of the primary skin tumour to mucoepidermoid tumours and to sweat gland carcinoma of the ductular epithelium will be considered in more detail.