There were 83 cases of usual interstitial pneumonia (UIP) in 3712 consecutive autopsy cases during 1972 to 1992 in Toranomon Hospital. Primary lung cancer had arisen in 40 cases of UIP in that period. The prevalence of lung cancer (48.2%) in UIP was significantly higher than that of lung cancers (9.1%) in the age-matched general population without UIP (P < 0.001). The prevalence of association of multiple lung cancer in UIP (20.0%) was also significantly increased. Thus, UIP showed a remarkable potency to develop lung cancers. The lung cancer cases in UIP had obvious smoking habits. Both the rates of smokers and the quantity of smoking were significantly increased in the lung cancer cases in UIP (P < 0.05). There was a distinct anatomical distribution of lung cancer in UIP. Most cancers in UIP (98%) arose in the peripheral area of the lung (P < 0.001, compared to lung cancer cases without UIP) with close relation to the honeycombing lesion. Studies on surgical specimens with small cancers showed that most tumors in UIP arose in the border area between honeycombing and the non-fibrotic area. Thus, the front of the remodeling of the lung is suspected to be a potential field of developing lung cancer. The chronic inflammatory process resulting in the remodeling of the lung may play an important part in the development of lung cancer in UIP under the circumstance of heavy smoking.