Serial magnetic resonance imaging (MRI) studies were performed in 27 patients undergoing primary radiation therapy for invasive cervical carcinoma, to assess the efficacy of this therapy. MRI findings included a high intensity area (HIA) in the uterine cervix and five parameters indicative of extrauterine spreading of the carcinoma: vaginal invasion, parametrial invasion, vesical invasion, rectal invasion and lymph node enlargement. In 26 of the 27 (96%) cases, the HIA was found prior to treatment, and remained in 17 (63%) cases at the end of the treatment. But in 10 of the patients with a residual HIA, this region resolved 3 to 8 months after treatment, and these patients had no evidence of residual tumor in the cervix on pathologic examination. The accuracy was lower in MRI examinations performed less than 6 months after the treatment (49%) than in examinations performed more than 7 months after the treatment (93%), suggesting that the HIA in the early post-treatment phase may be related to inflammatory changes. Findings indicative of extrauterine spreading decreased following treatment, but patients with recurrence had higher scores than those with no evidence of recurrence completion of the primary therapy. Furthermore, in 2 patients with local recurrence more than 1 year after treatment, the abnormal MRI findings reappeared and increased after the initial resolution of these findings with treatment. The present results indicate that MRI is clinically effective in evaluating the effects of radiotherapy in patients with cervical cancer.