Alpha-1-antitrypsin (alpha 1AT) deficiency is a hereditary disorder characterized in adults by a high risk for the development of severe destructive lung disease at an early age. The present study was designed to draw conclusions concerning the characteristics of a referral population of 124 patients with alpha 1AT deficiency and symptomatic emphysema. Typically, the alpha 1AT level was 30 mg/dl, and the alpha 1AT phenotype was almost always PiZZ. The individuals in this population were most often male, caucasian, and ex-smokers, and they had become dyspneic between 25 and 40 yr of age. Most routine blood tests were normal. The chest radiographs and ventilation-perfusion studies typically showed abnormalities with a lower zone distribution, and about one third of the study population had evidence suggestive of pulmonary hypertension. Lung function tests were typical for emphysema; the FEV1 and DLCO were the parameters most dramatically reduced, and the annual rate of decline of those parameters was greater than that of the general population. The cumulative probability of survival of this population indicated a significantly shortened lifespan with a mean survival of 16% at 60 yr of age compared with 85% for normal persons.