Adenoid cystic carcinomas (ACCs) and adenoid basal carcinomas (ABCs) are rare neoplasms of the uterine cervix that are currently regarded as distinct clinicopathologic entities. Accurate distinction between ABCs and ACCs is of clinical importance because of differences in their biological behavior. This study compares the morphologic, mucin, and immunohistochemical profiles of 18 cervical ACCs, 8 ABCs, and 1 combined ABC-ACC. Serial sections from the 27 cases were stained with hematoxylin and eosin, periodic acid-Schiff-diastase, mucicarmine, and alcian blue and subjected to a panel of immunoperoxidase markers, namely, MNF116, CAM 5.2, CK7, CK20, epithelial membrane antigen, carcinoembryonic antigen (CEA), S-100, HHF 35, laminin, and type IV collagen. One ACC was also examined ultrastructurally. Almost all patients were postmenopausal black women. The distinction between ABC and ACC was best made morphologically. Divergent epithelial differentiation was seen in 18 cases (11 ACCs, 6 ABCs, and 1 ABC-ACC). Six cases with intact surface epithelium showed a high grade squamous intraepithelial lesion. There was no significant difference in mucin staining. Both tumor types had a similar immunohistochemical profile, apart from type IV collagen and laminin staining, which occurred exclusively in relation to the extracellular basement membranelike material in the ACC. Eleven ACCs and three ABCs were S-100-positive, including the respective ACC and ABC components of the combined ABC-ACC. Eight of the S-100-positive neoplasms with ACC morphology also stained with HHF 35, suggesting myoepithelial differentiation. The latter was confirmed in one ACC examined ultrastructurally. The similar clinical profiles, apart from the different biological behavior, capacity for divergent differentiation, and the occurrence of ABC areas in some ACCs and vice versa suggest that these tumors may share a common histogenesis, forming part of a morphologic and biologic spectrum of basaloid cervical neoplasms of putative "reserve cell" origin. Circumstantial evidence suggests that ABC may be a precursor of cervical ACC.