Thirteen patients with a diagnosis of very well-differentiated endocervical adenocarcinoma were studied in order to characterize the histological and immunohistochemical features of minimal deviation adenocarcinoma (MDA). Five of these patients had neoplasms composed of structures almost identical to normal endocervical glandular patterns. These five neoplasms, representing MDA, were characterized by a haphazard proliferation of both large, claw-shaped glands, and smaller, slit-shaped, pointed glands. Focal mild cytologic atypia was identified in each case. Immunohistochemical stains displayed focal cytoplasmic carcinoembryonic antigen (CEA) in each neoplasm. Two of the five patients with MDA died of their neoplasms; both presented with advanced disease. Three well-differentiated adenocarcinomas lacked the deceptively bland appearance of MDA. Two of these three well-differentiated endocervical adenocarcinomas also contained CEA. Atypical endocervical gland proliferations originally diagnosed as MDA in five patients were reclassified as benign lesions on the basis of histologic pattern, findings after subsequent surgical procedures, and benign subsequent clinical courses. Of these five benign lesions, only reserve cell hyperplasia was found to contain CEA. Minimal deviation adenocarcinoma should be distinguished from the more common well-differentiated endocervical adenocarcinoma and from atypical benign lesions. Criteria for these distinctions are presented. While the histological appearance of an endocervical gland proliferation is the paramount basis for identifying an MDA, immunohistochemical staining represents a useful diagnostic aid.