The authors report two cases of primary popliteal venous aneurysm. This condition is rare. The lesion may be clinically asymptomatic and may remain unrecognised since it is discovered most often during the investigation of thrombo-embolic complications. The diagnosis is based upon ultrasonography and phlebography. Asymptomatic forms should merely be monitored. Apart from anticoagulants, the treatment of symptomatic forms is surgical. Methods remain controversial.