Sixty-six patients with chronic obstructive pulmonary disease (COPD) were evaluated for neuropsychological functioning. While the patients showed normal skills on broad intellectual tasks, they displayed mild cerebral deficits on several neuropsychological tests. Multiple regression analyses revealed that the neuropsychological test battery scores were significantly related to partial pressure of arterial oxygen (PaO2), and to degree of pulmonary impairment. Although the cognitive deficits were real, they were generally small. This result may explain why the widely assumed link between chronic lung disorders and cognitive deficit has been difficult to demonstrate. The general pattern was similar to deficits produced by chronic alcoholism and childhood asthma, with complex skills suffering the greatest insult. Because the cognitive deficits among COPD patients in stable condition are small, it is uncertain whether they have importance clinically or for accomplishing daily activities.