A population-based case--control interview study of cancer of the renal pelvis (74 cases and 697 controls) conducted in the Minneapolis--St. Paul metropolitan area showed cigarette smoking to be the major cause of this cancer. The odds ratio (OR) for cigarette smoking was 7.6 among males [95% confidence interval (CI): 2.2-31.5] and 5.8 among females (95% CI: 2.0-17.3), with the OR exceeding 10 for heavy smokers of both sexes. Long-term use of analgesics and several occupational exposures were also found to be risk factors. In addition, there were unexpected positive associations among females for heavy tea consumption and for use of estrogen medications, although the significance of these relationships remains to be clarified.