Placement of a radiation implant in patients with cervical cancer may be difficult because of distortion of the canal by tumor or fibrosis from previous radiation. The objective of this study was to determine whether ultrasound may be useful in recognizing or preventing complications associated with placement of an intracavitary implant. Transabdominal ultrasound was used during and after 20 intracavitary implants in patients with cervical cancers. In placing 20 implants, there were 9 placed in less than satisfactory relation to the anatomy of the uterus. In 6 patients, occult perforations occurred, with two-thirds not detected by the operator. Increased difficulty was seen at the time of placement of a second implant after external radiation. By using ultrasound, correction of the misplaced tandem could be made immediately without resorting to more invasive surgical approaches.