Modern intracavitary brachytherapy carefully combined with megavoltage external beam radiotherapy is responsible for the high cure rates achieved with radiation treatment of invasive cervical cancers. Pelvic disease recurrence is rare after treatment of patients with tumors < 5 cm in diameter, and even patients with massive tumors 8-10 cm in diameter are cured in 30-50% of cases. Inoperable adenocarcinomas of the endometrium and superficial cancers of the vagina are also effectively treated with intracavitary irradiation. The relative radioresistance of the uterus and vagina, physical advantages resulting from exploitation of the inverse square law, and the radiobiological advantages of low dose rate radiation have combined to make intracavitary irradiation a critical tool in the management of many gynecologic neoplasms.