In 40 women who had received radiotherapy for gynecologic carcinoma, biopsy was performed because recurrence of the tumor was clinically and/or cytologically suspected. Malignant tissue was found in two-thirds of the biopsy specimens. All the cytologic smears that preceded the biopsies were rescrutinized in order to establish criteria for recurrence of tumor. The initial indication of recurrence of squamous cell carcinoma was small cells with extremely dark, hyperchromatic nuclei. The nuclei were, as a rule, elongated, and their maximum diameter was about 8 micrometers. In the first smears these cells lay singly; later they were shed in clusters. The typical larger polymorphic cells without irradiation changes appeared later. Recurrence of adenocarcinoma was first indicated by more or less polymorphic, mainly ovoid naked nuclei about 20 micrometers in diameter with prominent nucleoli. The diagnosis of recurrent adenocarcinoma is often difficult since nuclear hyperchromasia may be absent in the early smears.