Potential risk factors in renal cell carcinoma (RCC) were studied in a case-control study of 315 RCC cases, 313 hospital and 336 population controls. Risk factors included body mass index, education, smoking, beverage use, and artificial sweeteners. High body mass index, when present at age 20 and maintained, was a significant risk factor in both men and women. The lower the educational levels attained, the higher the risk. There was a weak positive association with cigarette smoking, coffee drinking, tea drinking, and decaffeinated coffee. A strong negative association was found with ever use of alcohol and it was strongest for wine. A positive association was found with use of artificial sweeteners in men. These findings have increased our understanding of the etiology of this rare but increasingly important neoplastic disease in humans.