Bronchogenic cysts are closed sacs considered to be the result of an abnormal budding of the respiratory system. They are lined by ciliated epithelium and have focal areas of hyaline cartilage, smooth muscle, and bronchial glands within their walls. They are seldom seen in the adult, and most are thought to be asymptomatic and free of complications. During a 20-year period, 86 patients underwent resection of a bronchogenic cyst of the mediastinum (66 patients) and lung (20 patients). There were 47 women and 39 men whose ages ranged from 16 to 69 years. Seventy-two percent of patients (67% with mediastinal cysts and 90% with cysts of the lung) were symptomatic at the time of operation, and the majority had two or more symptoms. Despite extensive investigations, which in some cases included computed tomographic scanning (n = 12) and angiography (n = 22), a positive diagnosis was never made preoperatively even if it was suspected in 57% of patients. In nearly all patients, the operative approach was that of a posterolateral thoracotomy. All but two mediastinal bronchogenic cysts could be locally excised, but all bronchogenic cysts of the lung required pulmonary resection (lobectomy, 13; limited resection, 6; pneumonectomy, 1). Major operative difficulties were encountered in 35 patients, all of whom were symptomatic preoperatively. Thirty-three patients had a complicated cyst; the complications consisted of fistulization (n = 16), ulcerations of the cyst wall (n = 13), hemorrhage (n = 2), infection without fistulization (n = 1), and secondary bronchial atresia (n = 1). Overall, 82% of patients had a bronchogenic cyst that was either symptomatic or complicated or both.(ABSTRACT TRUNCATED AT 250 WORDS)