Background: Most programs favor single lung transplantation for emphysema. However, this is controversial, and we have favored bilateral lung transplantation, confining single lung transplantation mainly to use in older patients and those of small stature. Methods: A retrospective analysis was done of 119 consecutive lung transplantation procedures for emphysema at Barnes Hospital between 1989 and 1994 (50 single lung, 69 bilateral lung transplants) to (1) identify outcome differences between the two groups and (2) define the appropriate role of these two procedures. Results: The single lung transplantation group was older and had a higher proportion of female patients. However, baseline pulmonary function (forced expiratory volume in 1 second), arterial oxygen tension, and exercise tolerance (6-minute walk distance) were similar. After transplantation, 90-day mortality (single lung transplantation 10% versus bilateral lung transplantation 7.2%; p = 0.74) and duration of mechanical ventilation, intensive care unit stay, and hospitalization were similar. Both groups achieved a significant and sustained improvement in forced expiratory volume, arterial carbon dioxide tension, arterial oxygen tension, and exercise tolerance within 3 months. However, the improvements in forced expiratory volume, arterial oxygen tension, and exercise tolerance were consistently significantly better in recipients of bilateral transplants at and beyond 6 months. Obliterative bronchiolitis was equally prevalent in both groups. Survival was similar but showed a trend toward better late survival in recipients of bilateral transplants (5-year actuarial survival: bilateral lung transplantation 53% versus single lung transplantation 41%). Conclusions: We conclude that (1) both procedures are satisfactory options in emphysema, producing durable results; (2) bilateral lung transplantation is not associated with increased operative mortality or morbidity and achieves superior improvements in spirometry findings, oxygenation, exercise tolerance, and possibly late survival; and (3) the superior improvements in function (and late survival) after bilateral lung transplantation may be attributed to the presence of more pulmonary reserve after the onset of obliterative bronchiolitis.