Most hemodialysis patients exhibit renal anemia mainly due to erythropoietin deficiency as a result of impaired erythropoetin production in the kidney. However, erythrocytosis in patients with renal failure requiring hemodialysis is extremely rare. We report the development of erythrocytosis in a patient with a polycystic kidney disease oil hemodialysis for 13 years. She had erythrocytosis with increased serum erythropoietin levels despite severe secondary hyperparathyroidism, which is known to depress erythrocytosis. Since neither renal disease (renal cell carcinoma) nor extrarenal diseases (hypoxia, hepatoma, cerebellar diseases) linked with erythropoietin production could be proven, this case might be one with inappropriate idiopathic erythropoietin production after 13 years of hemodialysis, the longest duration of dialysis in the literature before erythrocytosis was observed.