A wide spectrum of histologic changes has been described throughout the female genital tract during pregnancy and in the postpartum period. Of these, the endometrial glandular changes referred to as the Arias-Stella reaction have classically been a diagnostic pitfall in histologic sections. Pregnancy-related changes are also reflected in cytologic material obtained from the cervix and vagina. Both glandular and stromal alterations may be seen. The changes involving endocervical glandular epithelium are often alarming enough to cause diagnostic difficulties, especially when the history of pregnancy is not provided. We report 13 cases where marked glandular changes led to diagnostic misinterpretations. These were characterized by cyto- and karyomegaly, a high nuclear to cytoplasmic ratio, round to oval nuclei with smudgy chromatin imparting a ground glass appearance, frequent intranuclear inclusions, and vacuolated to dense variable cytoplasm. The cytologic diagnoses ranged from "glandular atypia" to "suspicious for adenocarcinoma." Follow-up was available in 11/13 cases. In 9/11 cases, subsequent cervical smears on multiple occasions were negative. Cervical biopsies and/or dilatation and curettage in 4/11 cases did not show significant glandular abnormalities. The glandular changes encountered in cytologic material were similar to those described histologically in the Arias-Stella reaction involving the cervix. This similarity and the fact that these changes disappeared upon termination of the pregnancy favors the presumption that they represent the Arias-Stella reaction. Awareness of these changes during pregnancy and postpartum may prevent interpretive errors and unnecessary surgical procedures.