Women who have previously received radiotherapy (RT) for gynecologic cancer often suffer from vaginal fibrosis and stenosis. The success of “non-ablative” laser therapy for postmenopausal vaginal atrophy has led to the idea of testing the laser in patients submitted to RT. In this prospective observational study, we selected patients who underwent pelvic RT followed by vaginal laser treatment. We scheduled three treatment sessions (at T0–T1–T2) and three controls (at T1–T2–T3) one month apart. The follow-up (at T4) was carried out six months after the last treatment. Vaginal Health Index (VHI) and vaginal length were evaluated. Sexual function was assessed through Female Sexual Function Index (FSFI). Overall, 43 patients with severe vaginal shortening, atrophy and stenosis was enrolled and treated with intravaginal non-ablative CO2 laser. We observed a progressive increase in vaginal length of 9% (p = 0.03) at T2 and 28% (p < 0.0001) at T3; effects were maintained at T4 (p < 0.0001). After the first application VHI showed a significant improvement of 57% at T3 (p < 0.0001). The results were maintained at T4 (p < 0.0001). No changes were found in FSFI. All procedures were well tolerated. In conclusion, laser therapy improved vaginal length and VHI in women undergoing pelvic RT; prospective studies are needed.