Many cross-sectional and follow-up studies of large numbers of patients with hypertension have demonstrated an increased prevalence and mortality from renal cancer. We report the details of three patients with renal cell carcinoma from a series of 254 consecutive patients with malignant phase hypertension, an excess over the expected number reported from several large published series with non-malignant hypertension. In view of this excess we investigated the prevalence of hypertension in a series of 192 consecutive patients who presented with a diagnosis of renal cell carcinoma, in comparison with a local unselected population screening survey. Hypertension was found in 43% of the renal carcinoma patients and 20% of the local population, also a clear excess. The mechanism of the association between renal cancer and malignant and non-malignant hypertension is unclear.