An 85-year-old woman had a right-sided renal cell carcinoma removed 20 years ago. At haemoglobin concentration. Two years ago she had a syncope, at which time the haemoglobin concentration was 16.9 g/dl. Ultrasound and computed tomography (CT) revealed an extensive retroperitoneal space-occupying lesion, which however was not investigated further, and no therapeutic consequences were drawn. An erythrocytosis (7.5 x 10(6)/microliters) and elevated haemoglobin concentration (> 20 g/dl) were found when she was examined after a fall in which she had sustained only minimal injury. The retroperitoneal mass had slightly increased in size. Histological examination of a CT-guided fine-needle biopsy revealed metastases of the hypernephroid carcinoma. The serum erythropoietin concentration was increased (42.4 U/l) and failed to increase even after repeated venesections, indicating erythropoietin production by the late metastases of the renal cell carcinoma. There was no evidence for any systemic haematological disease. Six months after the diagnosis of metastases the patient died at home, presumably of a cerebrovascular accident.