A case of progressive pulmonary interstitial fibrosis following adjuvant lomustine (CCNU)-5-fluorouracil therapy for a colon carcinoma is reported. A close relationship between lomustine assumption and lung damage seems to emerge from the clinical, radiologic and histologic findings presented. On the basis of this experience and previous available data from literature, pulmonary toxicity must be regarded as a possible adverse effect of lomustine therapy.