Computed tomography (CT) can visualize the volume and shapes of the deep-seated tumors and is expected to predict the treatment outcome in a more quantitative manner. This study was undertaken to learn the prognostic significance of CT-provided information in the radiation therapy of carcinoma of the cervix. One hundred thirty-one CT evaluations were systematically applied to 87 patients having carcinoma of the cervix uteri. The cervical mass volume was measured by CT at a certain phase or phases of treatment and was analyzed in relation to their local control at 3 years and the survival at 5 years. The initial volume, measured at the beginning of radiation therapy, was not a significant prognostic guide for the local control. However, the second volume, the volume of cervical lesion measured immediately after the completion of external irradiation, proved to be a prominent prognostic factor for both the 3-year local control and 5-year survival, regardless of the clinical stage. In 52 patients whose second volume was less than 38 cm3, 47 patients (90.4%) were locally controlled for 3 years or more after radiation therapy, whereas 17 of 23 patients (73.9%) whose second volume exceeded 38 cm3 failed in the local control. Five-year actuarial survival rate was 53.1% plus or minus 6.2% in the former group and 26.1% plus or minus 9.6% in the latter group. CT-aided volumetry provides for an early prediction of treatment failure in radiation therapy for cervical carcinoma.