We describe and compare the computed tomographic (CT) manifestations of radiation fibrosis and recurrent neoplasm and consider the potential application of CT in the follow-up of patients after radiotherapy for bronchogenic carcinoma. Thirty-one patients were evaluated in this retrospective study. The CT findings in 20 patients with radiation fibrosis were compared with those in 11 patients with recurrent tumor. In 19 of the 20 patients with radiation fibrosis, CT allowed demonstration of consolidation, with a straight lateral margin and containing ectatic air-containing bronchi. In 9 of the 11 patients with recurrent tumor, CT showed a soft tissue mass with a convex lateral border and without air-containing bronchi. Twenty of the 31 patients had a suspected recurrence on plain chest radiographs. CT permitted accurate differentiation between radiation fibrosis and recurrent tumor in all patients, with the exception of two who had large pleural effusions. Because of its great specificity, CT appears useful in complementing chest radiographs in the follow-up of patients after radiotherapy.