Lytic bony lesions which histologically consist of proliferation of well-differentiated small endothelial-lined blood or lymph vessels separated by loose connective tissue have been described in humans. These lesions have been termed skeletal angiomatosis, hemangiomas, and vascular malformations. 1.2.e8 This report describes a similar disease in three young cats. Case 1 was a 20-month-old male domestic long-haired cat which presented at 17 months of age for posterior paresis that was responsive to antibiotics and steroids. It re-presented at 20 months for bilateral proprioceptive deficits. Hemogram was normal, and feline leukemia virus tests were negative. Myelogram indicated obstruction of contrast material at T2 with decreased bony density at T,. Owners elected euthanasia. At necropsy the referring veterinarian found a pinkish-tan 1.0 x 0.5 x 0.3 cm extradural mass protruding into the spinal canal. The spinal cord in the region was compressed. Case 2 was a 1-year-old castrated male domestic shorthaired cat which presented at 14 months and again at 15 months of age for pain and progressive posterior paresis and ataxia. Plain radiographs showed a lytic area at TI,, I; a myelogram was compatible with extramedullary compression of the spinal cord at TI I. A surgical dorsal decompression at TI, and TI, was done. The bones of the dorsal laminae and articular facets appeared to the surgeons to be “thickened but porotic” and were felt to be the cause ofthe cord compression. Portions of these bones were submitted for histopathologic examination. Three months post-operatively the cat was free of clinical disease. Case 3 was a 15-month-old female domestic long-haired cat which had a 1 -year history of posterior paresis which was progressively less responsive to steroid therapy. Plain radiographs revealed a moth-eaten appearance of bone at T, involving the dorsal vertebral body, pedicles, and laminae. Myelogram indicated an extradural compression at T,. Owners elected euthanasia. The formalin-fixed and decalcified specimen of T, revealed red-brown irregular masses within the dorsal and transverse spinous processes on cut section. A 0.6 x 0.4 x 0.6 cm red-brown mass protruded into the spinal canal and compressed the adjacent spinal cord (Fig. 1). Histologically, sections from all cases were similar. Vessels of varying sizes with endothelial cells, prominent pencytes, and variable amounts of smooth muscle were present within a loose connective tissue stroma separated by bony trabeculae (Fig. 2). Some of these vessels, interpreted to be arterial, contained red blood cells; others were empty. The bony trabeculae were predominantly lamellar with moderate numbers of osteoblasts and infrequent osteoclasts present. Hemopoietic elements were displaced by vascular proliferations and stroma. Vascular proliferations extended along marrow spaces and vascular channels to the periosteum in case 1, and focally infiltrated a nerve in case 3, where extensive remodeling of surrounding bone was also found. These bony and vascular proliferations corresponded to the masses causing gross spinal cord compression and were contiguous with the vertebrae. The lytic nature of the masses seen radiographically could not be appreciated microscopically. Although the vascular proliferations in these cases were aggressive, they differed from recognized vascular neoplasms because there were multiple cell types involved: endothelial, perithelial, smooth muscle, and fibrous. Nomenclature for human vascular lesions does not provide a well-defined category for the proliferations in these cats. Skeletal angiomatosis is a term used in human pathology to