Four case studies of patients with angiographically documented pulmonary arterial aneurysms are presented. In two cases, Behcet's disease was diagnosed; one case corresponded to the syndrome described by Hughes and Stovin, that is, venous thrombosis especially of the vena cava accompanied by singular or multiple pulmonary arterial aneurysms in young patients; and the last case could best be described as an association of the two. Our observations lead us to question the existing notions concerning the relationship between Behcet's disease and Hughes-Stovin syndrome-the clinical, angiographic and histologic aspects of the vascular manifestations are comparable. Typically the two diseases run similar courses with death resulting frm the rupture of the aneurysms and massive hemoptysis. These case studies cast certain doubts as to the effectiveness of the corticosteroid treatment usually prescribed. Finally, we suggest that Hughes-Stovin syndrome might be, in fact, a manifestation of Behcet's disease.