Urticarial skin lesions may occur in patients as a manifestation of necrotizing vasculitis. We describe a series of forty patients with idiopathic chronic urticaria and histologic features of necrotizing vasculitis. On the basis of clinical evaluation, we have classified urticarial vasculitis into two major groups: (1) hypocomplementemic (sixteen patients, ten of whom had evidence of renal disease) and (2) normocomplementemic (twelve patients with systemic disease and twelve with only cutaneous involvement). Most patients with hypocomplementemic presented with arthritis, and some had abdominal pain or airway compromise. Although patients with normocomplementemia and systemic disease had a less severe clinical course, four exhibited renal disease that was characterized by microhematuria and proteinuria. Direct immunolluorescence microscopy of the skin aids in assessing renal involvement in some cases of hypocomplementemic urticarial vasculitis, particularly when IgG and IgM are deposited at the basement membrane. There seems to be a spectrum of disease in urticarial vasculitis, ranging from benign cutaneous lesions to systemic disease.