Forty-eight cases of thrombosis of major veins of the upper extremity have been studied. In 17 patients primary thrombosis occurred following effort, prolonged compression, or without recognized cause. Thirty-one patients experienced venous thrombosis secondary to thrombophlebitis of varying etiology, or underlying systemic disease. On various nonoperative treatments, all acute manifestations of the disorder disappeared within a few days of treatment. Late follow-up information on 31 patients showed residual disability in 74%. Late venography demonstrated continuing occulsion of the major trunks in ten of 11 patients examined an average of 6.6 years following the initial episode. Venous pressure was elevated significantly in symptomatic patients, but not in asymptomatic ones. Because of the long-term disability experienced by the affected patients, new therapeutic approaches should be considered.