Although there is good evidence that emotions are associated with chronic airways obstruction, evidence for the influence of psychological factors on the level and decline of pulmonary function is sparse. Optimism has been linked to enhanced well-being, whereas pessimism has been identified as a risk factor for poor physical health. This investigation examines prospectively the effects of optimism versus pessimism on pulmonary function. Data are from the Veterans Administration Normative Aging Study, an ongoing cohort of older men. In 1986, 670 men completed the revised Minnesota Multiphasic Personality Inventory from which we derived the bipolar Revised Optimism-Pessimism Scale. During an average of 8 years of follow-up, an average of 3 pulmonary function exams were obtained. Men with a more optimistic explanatory style had significantly higher levels of forced expiratory volume in 1 sec (FEV1) and forced vital capacity (both p < .01). Interactions between time and optimism suggested that rate of decline in FEV1 over time was slower in men with a more optimistic explanatory style relative to men who were more pessimistic. These data are the first to link optimism with higher levels of pulmonary function and slower rate of pulmonary function decline in older men, a protective effect that is independent of smoking.