Purpose <p>Pelvic radiotherapy (RT) causes tissue injury which could lead to vaginal problems including dryness, shortening, and tightening of the vagina, causing discomfort, and affect sexual activity. In this longitudinal, prospective study, the association between pelvic RT and sexual function were studied in primary cervical cancer and in primary uterine tumor patients.</p> Methods <p>This prospective longitudinal cohort study comprised patients with primary cervical cancer and primary uterine tumors with pelvic radiotherapy (RT). Seventy-nine cervical cancer and 43 uterine tumor patients were included from May 2014 to February 2019. Patients completed questionnaires for global health status and sexual functioning before RT start and at 3 and 12&#xa0;months after RT.</p> Results <p>In primary cervical cancer patients, the sexual activity was significantly higher in patients with pelvic RT alone compared to patients with pelvic RT + cervical brachytherapy/boost at 3&#xa0;months (<i>P</i> = 0.007, 34.6% vs. 73.3%) and&#xa0;12 months after RT (<i>P</i> = 0.054, 45.7% vs. 76.9%). No significant relationship was found in primary uterine tumor patients. At 12&#xa0;months after RT, 52.5% of the cervix and 42.3% of the primary uterine tumor patients were sexually active. Of the cervical cancer patients, 81.8% reported symptoms as dry vagina 12&#xa0;months after RT. Local estrogens did not improve the sexual activity in cervical cancer or uterine tumor patients after RT.</p> Conclusion <p>In cervical cancer patients, the sexual activity was significantly higher with pelvic RT alone compared to pelvic RT + cervical brachytherapy/boost. Better medical interventions are needed to reduce the sexual symptoms.</p> Implications for Cancer Survivors <p>Reduced sexual activity in gynecological cancer survivors with curative pelvic RT. For the future, improved medical interventions are needed to decrease the sexual symptoms.</p>