Mucinous syringometaplasia (MS) is an unusual skin lesion of unknown etiology, characterized histologically by epidermal invaginations lined by mucin-laden goblet-like cells and by nonkeratinized squamous cells. The present case study was performed to elucidate further the characteristics of this lesion using immunohistochemistry and electron microscopy. The mucin-laden cells in the MS lesion stained positively for carcinoembryonic antigen, epithelial membrane antigen, and low molecular weight keratins. The ultrastructural examination, which was performed on deparaffined sections, revealed two morphological variants of mucous granules. Electron-dense mucous granules predominated in the mucus-containing cells, which were situated among the keratinocytes adjacent to the epidermal invaginations, mostly in the lower parts of the epidermis. Larger, electron-lucent granules containing flocculent material were found more abundantly in the cells lining the epidermal invaginations. Also, some of the mucus-containing cells showed bundles of tonofilaments; structures that appeared to be isolated short, stubby microvilli; and attachments to adjacent mucus-containing cells and keratinocytes by desmosomes. The ultrastructural and immunohistochemical findings in our case suggest that the mucinous changes occurred as a metaplastic process in the resident epidermal cells and were accompanied by changes in cellular antigen expression resembling those of simple secretory epithelium.