Objective To analyze the performance of cytologic examinations for the diagnosis of adenocarcinoma in situ (AIS) through the correlation between the cytologic and histologic findings. Study Design This study included 60 patients followed at the Brazilian National Cancer Institute from November 1998 to December 2007, with the cytopathologic diagnosis of AIS. The percentage of agreement between cytologic and histologic findings was evaluated. Results Histologic study confirmed AIS in 28.3% (17/60) and invasive endocervical adenocarcinoma in 38.3% (23/60) of the cases. In 21.7% (13/60) of the patients, the histologic examination revealed cervical intraepithelial neoplasia (CIN) 2/3 and in 5.0% (3/60) squamous invasive carcinoma; in the remaining 5.0% (3/60) the diagnosis pointed to other neoplasms, and 1.7% (1/60) showed exclusively benign squamous cell lesions. Cytology identified lesions in 98.3% of the patients; 51% was intraepithelial. Conclusion Although cytomorphologic criteria for diagnosis of AIS have been published, there was significant difficulty in interpreting glandular lesions. However, despite the fact that cytology has shown a poor performance in identifying glandular lesions, in almost all cases (98.3%) the presence of a clinically significant injury was detected. As knowledge of this diagnosis increases, better performance is expected. (Acta Cytol 2009;53:558-564)535558564