PURPOSE: To evaluate magnetic resonance (MR) imaging in the planning of radiation therapy for patients with cervical cancer. MATERIALS AND METHODS: MR imaging was performed in 15 patients with predominantly advanced cervical carcinomas. Skin markings of the radiation ports were labeled with MR-detectable tubing and beads to assess the adequacy of port placement. Volume and extent of tumor at MR imaging were compared with those at physical and computed tomographic (CT) examinations. RESULTS: Tumor involvement of normal structures (parametrium, vagina, endometrium) was more extensive at MR imaging than at clinical examination in six patients (40%) and at CT in five patients (33%), resulting in modification of the radiation fields in eight patients (53%). Tumor size was larger on MR images than at clinical examination in 11 patients (73%). CONCLUSION: MR imaging can depict tumor volume and better delineate the extent of involvement than physical and CT examination. This can be useful for placement of radiation ports, especially when small boost fields are used.