Vasculitis applies to a heterogeneous group of diseases characterised by damage of blood vessels with infiltration of the vessel wall by inflammatory infiltrate, which leads to occlusion of the blood vessel and subsequenttissue ischemia. Necrotising arteritis occurs as a primary phenomenon in connective tissue disorders, especially in polyarteritis nodosa and as a secondary phenomenon in inflammatory or infectious general conditions. This process, which is related to local or systemic vascular inflammation, produces vessel and tissue necrosis with typical leucocytic infiltration, leucocytoclasia, haemorrhage and fibrinoid change, In both settings necrotising arteritis induces ischaemic nerve lesions responsible for focal or multifocal neuropathy in 75% of the patients with primary vasculitis. Search for vasculitis is the best indication for nerve and muscle biopsy since histological demonstration of vasculitis is necessary. In 82% of our patients with histologically confirmed necrotising arteritis of the type observed in polyarteritis nodosa, vasculitis was of the primary type. Most patients had classic polyarteritis nodosa. Necrotising arteritis was associated with rheumatoid arthritis in 21% of our patients. Peripheral neuropathy was the only manifestation of vasculitis in a large fraction of our patients with primary vasculitis. Necrotising arteritis invariably affects epineurial arteries and induces ischaemic nerve lesions, with axonal degeneration of the vast majority of nerve fibres. Mononeuropathy was present in 15% of the patients, mononeuritis multiplex in 57%, distal symmetrical neuropathy in the others. The peroneal nerve was the most commonly affected territory. The neurological manifestations and the course of Churg-Strauss syndrome, a variant of polyarteritis nodosa, are very similar to those occurring in polyarteritis nodosa. In 18% of the 400 neuropathic patients with histologically demonstrated necrotising arteritis, vasculitis occurred in the setting of a symptomatic non-connective tissue disorder (non-CTD). The later included 29 patients with active viral infection (HIV, CMV, HTLV-1 infections and chronic B and C viral hepatitis); 14 patients with multifocal neuropathy associated with type 2 diabetes mellitus; 13 patients with monoclonal gammapathy, including one patient with Waldenstrom's disease and one with myeloma. 11 patients had a malignant haemopathy, including the 2 with malignant monoclonal gammopathy; 2 had familial amyloidosis and 8 sarcoid neuropathy. 7 patients had a mononeuritis, 33 mononeuritis multiplex; 44 had a distal sensorimotor neuropathy. In patients with non-connective tissue disorder, necrotising arteritis was detected in 70/73 nerve specimens and in 27/73 muscle specimens (19 in both specimens). Necrotising arteritis was more frequently found in nerve specimens of patients with non-connective tissue disorder (95%) than in classical polyarteritis nodosa (66%); muscles were affected in only 35% of the non-CTD patients versus 66% in patients with primary vasculitis. Thus necrotising arteritis which represents a treatable cause of neuropathy, and the main indication for nerve biopsy, can induce ischaemic nerve lesions in connective as well as in non-connective tissue disorder.