An association between transitional cell tumors (TCT) and abuse of compound analgesics has been established during the past two decades. Recently thickening of basement membranes around subepithelial capillaries, known as capillarosclerosis, has been reported as a change in the urinary tract pathognomonic for a long-standing abuse of compound analgesics. Therefore the authors reviewed pathologic and clinical data in 59 patients treated for TCT of the renal pelvis or ureter. Capillarosclerosis was found in nine cases (15%) of the TCT group but not in any of the cases selected as controls. Capillarosclerosis is suggested as a valuable marker, which always should be looked for in bladder biopsy specimens. Whenever present it should arouse suspicion of analgesic abuse, and the associated increased risk for developing TCT of the renal pelvis or ureter should be borne in mind.