In a series of 300 cases of PV evaluated and treated over the last 12 years, 5 cases had a kidney carcinoma, either previously treated (2 cases) or discovered at the same time as the PV (3 cases). In all these cases, the blood disease had the criteria of a myeloproliferative syndrome (abnormality of three cell-lines), was not influenced by nephrectomy and evolved in the long term like a primary PV. No kidney cancer was observed during follow-up of the other 32P treated PV patients. There appears to be an abnormal association between PV and kidney cancer which needs confirmation in larger series and would justify a prospective evaluation.