Eighteen patients with chronic obstructive pulmonary disease (COPD) were administered a series of pulmonary, neurological, and neuropsychological measures to test if there was an effect of COPD on neurological and cognitive functioning. Overall, there was no evidence of general dementia in this sample. Measures of immediate and delayed memory, complex attention, and speed of information processing correlated highly with arterial carbon dioxide partial pressure and, to a lesser extent, with oxygen partial pressure. Measures of language abilities, perceptual-motor functioning, and simple attention generally were not related to arterial gas pressures. A similar pattern of findings was obtained when group differences were examined between participants classified as severely hypoxic or mildly hypoxic, although group differences were mitigated by premorbid IQ differences. Hypoxia in COPD results in a relatively focused pattern of impairment in measures of memory function and tasks requiring attention allocation. The memory dysfunction may be related to involvement of limbic memory regions necessary for explicit memory. The attentional deficits were attributed to diffuse brain involvement resulting in reduced resource allocation. Early diagnosis and treatment of the hypoxia is essential.