Forty-two lung cancer patients with COPD (7.9% of 534 lung cancers), and 84 age- and sex-ratio-matched controls who were randomly selected from lung cancer patients without COPD were examined. Lung cancers with COPD consisted of 25 cases of squamous call carcinoma (59.5%), 11 of adenocarcinoma (26.2%), 2 of small-cell carcinoma (4.8%), and 4 of large-cell carcinoma (9.5%). Squamous cell carcinoma occurred more in patients with COPD than in controls (35.7%) (p less than 0.01). In squamous cell tumors with COPD, 12 cases (48.0%) were centrally located and 13 cases (52.0%) were peripherally located. Squamous cell carcinoma of peripheral origin occurred more in patients with predominant emphysema (76.9%) than controls (36.7%) (p less than 0.05). Our results suggest that the COPD patients with predominant emphysema may be at greater risk for squamous cell tumors of peripheral origin.