The clinical, histologic, and immunohistochemical features of six cases of hemorrhagic adrenal pseudocysts are reported together, with a review of the English literature on this topic since 1950. The mean age at presentation was 57 years (range, 30-72 yr). There were four men and 2 women. The average cyst size was 9.2 cm (range, 6-16 cm). In four patients, the hemorrhagic adrenal pseudocysts were incidental findings. The remaining two patients presented with an abdominal mass and hypertension, respectively. The hemorrhagic pseudocysts were unilocular cystic masses surrounded by a fibrous capsule and containing abundant amorphous material, blood, and fibrin. Numerous dilated, thin-walled, vascular channels that stained strongly for Factor VIII-related antigen, collagen IV, laminin, Ulex europaeus agglutinin I lectin, and CD34 were present within the fibrous capsule, cyst contents, and surrounding residual adrenal gland. These findings support a vascular origin for these lesions, and they are thought, therefore, to be related to endothelial adrenal cysts. The literature review of 111 vascular adrenal cysts (85 hemorrhagic pseudocystic type and 26 endothelial type) showed similar clinical features. The mean age at presentation was 44.5 years (range, 5 d-95 yr), with a female predominance (62%). The most common clinical presentation was abdominal pain (35%), followed by incidental findings (32%). There were no significant clinical differences between hemorrhagic and endothelial type cysts. In some cases, the presence of intracystic islands of cortical cells can cause diagnostic confusion with adrenal cortical tumors. The presence, however, of a rich intracystic and capsular vascular network, normal-appearing islands of cortical cells, and abundant thrombotic fibrinous material, rather than necrotic tumor cells, should rule out the possibility of a degenerating adrenal cortical neoplasm.