The objective of this study was twofold: (1) to document the prevalence of depression and anxiety in patients with moderate or severe chronic obstructive pulmonary disease; and (2) to determine whether the presence of depression or anxiety adversely affected the functional capabilities of the patient as reflected by the distance he could walk in 12 minutes. Forty-five patients with an FEV1 less than 1,250 ml underwent pulmonary function testing including spirometry, single breath diffusing capacity, and arterial blood gas determinations. The degree of depression was assessed by the Beck depression inventory, while the degree of anxiety was assessed by the State-Trait anxiety inventory. Forty-two percent of the patients had significant depression, while only 2 percent of the patients had significant anxiety. There was a highly significant correlation between the depression scores and the anxiety scores (r = 0.81, p less than 0.001). There was no significant correlation between the level of depression or anxiety and the distance that the patient could walk in 12 minutes. From this study, we conclude that the prevalence of depression in patients with moderate or severe COPD approaches 50 percent while the incidence of anxiety is much lower (2 percent).