Polymyositis is characterized by a T-cell-mediated and MHC-I-restricted cytotoxic process, whereas dermatomyositis is a primitively vascular disease with microangiopathy mediated by the complement C5b-9 membranolytic attack complex. We have tried to estimate the frequency of vascular abnormalities in polymyositis as defined by Bohan and Peter. We have retrospectively studied 17 patients with dermatomyositis and 15 patients with polymyositis. Vascular abnormalities have been defined by clinical, capillaroscopic and histologic (muscle biopsy and minor salivary glands biopsy) features. After clinical features, 5/17 dermatomyositis had a Raynaud's phenomenon, against 6/15 polymyositis. Digital necrosis has been observed for 2/17 dermatomyositis and 2/15 polymyositis. In capillaroscopy, 14/17 dermatomyositis had a microangiopathy with or no enlarged capillary loops, against 7/15 polymyositis. None of these polymyositis had enlarged capillary loops. The muscle biopsy showed a predominantly perivascular or perimysial inflammatory infiltrate (vascular process) for 10/16 dermatomyositis against 4/13 polymyositis; a perifascicular atrophy for 3/16 dermatomyositis against 2/13 polymyositis. The histological study of minor salivary glands, showed vascular lesions for 2/11 dermatomyositis and for 1/8 polymyositis. Finally, Bohan and Peter's classification is now inadequate to distinguish between dermatomyositis and polymyositis. Indeed, some dermatomyositis sine dermatitis, may exist and be recognized by their vascular features. To distinguish between dermatomyositis and polymyositis is important, to evaluate the risk of cancer which is more frequent in dermatomyositis.