The objective of this study was to prospectively assess pulmonary venous anastomosis by transesophageal echocardiography after lung transplantation. Thrombus formation at the pulmonary venous anastomotic site after lung transplantation may have catastrophic consequences, including allograft failure and stroke. Eighty-seven consecutive adult lung transplant recipients underwent transesophageal echocardiography within 48 hours after surgery. Thrombosis of a pulmonary vein was diagnosed in 13 (15%) of 87 patients in the early postoperative period after lung transplantation. Mean thrombus width was 0.9 +/- 0.4 cm (range, 0.5 to 1.7 cm), with an average peak flow velocity at the site of obstruction of 127 +/- 23 cm/s (range, 90 to 150 cm/s). Five patients with pulmonary vein thrombosis died in the perioperative period, yielding a 90-day mortality rate of 38%. Larger thrombus size and greater acceleration of flow through a narrowed pulmonary vein correlated with poor clinical outcome. During each year of the study, the incidence of pulmonary vein thrombosis declined progressively. Pulmonary vein thrombosis is a potentially ominous complication in the early postoperative period after lung transplantation. Transesophageal echocardiography is a valuable tool for detecting abnormalities of the pulmonary venous anastomosis. Thrombus size and flow velocity at the anastomotic site may guide prognosis and clinical management. Complications of the pulmonary venous anastomosis are in part technical in nature.