['The Banff 1997 classification of renal allograft pathology identifies arteriolitis as a finding of uncertain significance. We sought to improve our understanding of arteriolitis by correlating its occurrence with histopathological and clinical parameters.', 'Twenty allograft kidney biopsies from 19 patients, showing arteriolitis, were identified. Arterioles were defined as small vessels with: (1) wall thickness of 1-3 myocytes; (2) diameter less than one-third of an adjacent glomerulus; and (3) discontinuous or absent elastica. Arteriolitis was defined as mural infiltration by lymphocytes. Other histological findings were categorized according to the Banff 1997 working formulation. Ten biopsies (50%) showed type IIA rejection, seven (35%) showed type I rejection, and three (15%) showed borderline change. Two patients with borderline change had acute rejection in the next biopsy. None of the seven patients with type I rejection had previous or subsequent type II rejection on biopsy. A total 11/20 biopsies (10/19 patients) showing arteriolitis had type IIA rejection in the index or next biopsy. On follow-up, graft loss due to rejection occurred in 5/19 (26%) patients (median 126 days); all had shown type IIA rejection on a previous biopsy. Chronic allograft nephropathy developed in a further 4/19 (21%) patients (median 157 days), of whom three had shown only type I rejection on biopsy.'] Is arteriolitis in renal transplant biopsies associated with poor graft outcome?