Seventy cases of histologically confirmed adenocarcinoma in situ (AIS) of the cervix uteri have been predicted in this laboratory using cytologic criteria, which are illustrated in this paper. The architectural features that were of primary diagnostic importance included an exfoliation pattern consisting of sheets of cells and tissue fragments in the form of cellular strips and rosettes. Nuclear criteria allowed the distinction of AIS into well-differentiated and poorly differentiated types. The former showed nuclear enlargement, an oval nuclear shape, hyperchromasia and moderate-to-coarse granularity as usual features. In the latter, nuclear enlargement was even greater, with an oval-to-round shape, prominent nucleoli and chromatin that was usually only finely granular. Variant patterns of AIS included endocervical, endometrioid and intestinal subtypes, each with characteristic cytologic appearances that correspond closely with their histologic appearances. The evolution of the description of AIS reveals a range of precursor lesions that may match the range of invasive adenocarcinomas originating in the cervix. This suggests that invasive adenocarcinoma of the cervix uteri could be preventable as is its more common squamous counterpart.