A population-based, case-control study was conducted in Los Angeles County, California, to investigate the inter-relationships of obesity, hypertension and medications in relation to renal cell carcinoma (RCC) risk. A total of 1204 RCC patients and an equal number of neighbourhood controls were included. Obesity was a strong risk factor for RCC. A fourfold increase in risk was observed for those with usual body mass index (kg m(-2)) of > or = 30 vs < 22. A history of hypertension was another strong, independent risk factor for RCC [odds ratio (OR) = 2.2; 95% confidence interval (CI) = 1.8, 2.6]. There was little evidence that use of diuretics was directly related to RCC development. Use of diuretics for reasons other than hypertension (primarily for weight control) was unrelated to risk among self-reported normotensive subjects (OR = 1.2; 95% CI = 0.7, 2.2). Among hypertensive subjects, heavy users of diuretics experienced similar risk as light users (OR = 0.9 among subjects with lifetime dose of > or = 137 g compared with those with lifetime dose of < 43 g). Similarly, normotensive subjects who took non-diuretic antihypertensives regularly showed no increased risk for RCC (OR = 1.1; 95% CI = 0.6-1.8), and intake among hypertensive subjects did not further increase their risk. Regular use of amphetamine-containing diet pills was associated with a twofold increase in RCC risk (95% CI = 1.4-2.8) and the risk increased with increasing dose of amphetamines. However, the fraction of cases possibly related to this exposure is small (population-attributable risk = 5%).