AbstractAmong adenoid cystic carcinomas of salivary glands (ACCs), the solid basaloid type has a poor prognosis similar to that of undifferentiated adenocarcinomas. We studied 24 cases in immunohistochemistry using antibodies reactive with keratins of various molecular weights, vimentin, S‐100 protein, and its A and B subunits. Our findings were correlated with the histological pattern and with the variable degree of differentiation of these carcinomas. In comparison with other types of ACC, intermediate filament proteins in this group were weakly expressed. The co‐expression of cytokeratin and vimentin was noted in some cases. Additional features noted were the presence of cribriform cavities associated with solid lobules and areas of necrosis giving a comedocarcinomatous pattern. In these two variants, cells characterized by the dual expression of cytokeratin and S‐100 protein were seen. In the highly malignant anaplastic variety, only a few cells were weakly positive with antisera to cytokeratin and vimentin. This group shows similarities to undifferentiated adenocarcinomas of salivary glands. Such similarities could be explained by the common origin of these tumours from intercalated