A review of 389 primary adenocarcinomas of the uterine cervix [in humans] was conducted. After histologic classification, each was evaluated for the presence of squamous dysplasia and carcinoma in situ. Squamous epithelium was not present in 159 instances, but 230 cases were eligible for further evaluation. Squamous intraepithelial neoplasia was present in 99 (43%) of these: severe dysplasia and carcinoma in situ comprised > 1/2 of the cases. The frequency of squamous intraepithelial neoplasia in the major subtypes of primary adenocarcinoma is discussed. The term cervical (squamous) intraepithelial neoplasia includes all cases of dysplasia (mild, moderate and severe) and carcinoma in situ.