We studied a random sample of 436 subjects with TOS aged 18 to 60 years, to assess the prevalence of respiratory involvement four years after onset of the syndrome. Clinical evaluation together with chest roentgenograms, electrocardiogram and functional respiratory tests were carried out. Respiratory involvement occurred in 390 (89.4 percent) individuals and was the most common abnormality detected, followed by neurological disorders in 289 (66.3 percent), osteoarticular symptoms in 171 (39.2 percent), psychiatric disorders in 96 (22 percent), hepatic involvement in 91 (20.9 percent), and sclerodermatous sequelae in 89 (20.4 percent). Among patients with respiratory involvement, dyspnea and cough were the most common complaints. Decreased VC was observed in 151 (34.6 percent) patients and reduced transfer factor of CO in 95 (21.8 percent) patients. Airway obstruction and alveolar hypoventilation were observed only in nine (2.1 percent) patients. Six (1.4 percent) patients suffered from pulmonary artery hypertension.