In this study of 58 cervical in situ and invasive adenocarcinomas, the diagnostic accuracy of cervical biopsies was found to be closely related to the extent and the degree of differentiation of the neoplasm. Biopsies of in situ and early, well-differentiated adenocarcinomas were often limited in amount, precluding an accurate assessment of stromal invasion. In such cases, a comprehensive sample, e.g., by conization, was required to establish the diagnosis. Invasive adenocarcinoma could be distinguished from the in situ change by the loss of branching pattern of normal endocervical glands, a marked variation in the size and shape of the glands, and a complex papillary or solid growth pattern. The presence of a desmoplastic reaction further supported the invasive nature of the neoplasm.