Appendiceal vasculitis and splenosis in a young women provided pathologic evidence that a systemic necrotizing vasculitis preceded the onset of hairy cell leukemia by at least six years. As in other patients who have had both diseases, florid polyarteritis nodosa developed during the course of the malignancy. However, the antecedent vasculitis, as well as the coincidence of these rare diseases, indicate that systemic vasculitis does not necessarily result from hairy cell leukemia as previously reported and suggest that the two diseases might share a common pathogenesis or predisposing factor.