A total of 480 lungs operated for lung cancer were reviewed in an attempt to clarify the characteristics of idiopathic chronic interstitial pneumonia (UIP), seen in the cancer bearing lungs. UIP was identified in 30 cases (6.3%). The mean patients age was 68 years, and 26 cases were male. Squamous cell carcinoma was the dominant tumor type (17 cases) and the lower lobe was the dominant location (18 cases). All cancers were situated in the periphery of lungs which had UIP, but not necessarily in the center of the fibrosis. According to extent, UIP is divided into two categories, localized and diffuse types. Twenty-seven cases had localized type UIP. UIP can be divided into another three categories, according to its microscopic findings; Intramural (IM), emphysematous (E), and intraluminal (IL) types. Eight cases had IM-type and 22 cases had E-type UIP. Some IM-type UIP cases showed only increased density of the subpleural space on CT, without visible cysts. E-type UIP cases had no decrease of lung capacity, and showed various sized cysts on CT. Some cases showed postoperative worsening of UIP and acute exacerbation. We feel that the existence of localized UIP (especially emphysematous type) is important in the early detection of cancer, and as a cue for careful post-operative management to prevent serious complications.