Experimental studies have demonstrated that calcium is an essential molecule in modulation of erythropoiesis. The aim of this study was to investigate the role of serum calcium levels on the development of posttransplantation erythrocytosis (PTE) among renal transplant recipients. We enrolled 155 patients (36 females/119 males; mean age, 34.9 +/- 9.7 years) with normal graft function who underwent renal transplantation between 1999 and 2002. All of the demographic features and various laboratory parameters were retrospectively analyzed as possible factors associated with erythrocytosis. PTE appeared in 43 (27.7%) patients during the follow-up period. Sixty-three (40.6%) patients developed hypercalcemia (corrected serum calcium level >= 10.2 mg/dL). Serum calcium levels tended to increase in patients with PTE, but significantly decreased in patients without PTE (10.6 +/- 0.6 vs 9.8 +/- 0.5 mg/dL; P < .0001). Similarly, hypercalcemia was more common among patients with PTE compared with patients without PTE (74.4% vs 27.7%; P < .0001). Hypercalcemic patients had a significantly higher frequency of PTE than normocalcemic patients (50.7% vs 11.9%; P < .0001). There were no differences in other laboratory and demographic data between the patients with and without PTE (P > .05). These findings suggest that hypercalcemia may lead to increased PTE in renal transplant recipients.