Background. To date, the clinical trials of tacrolimus (TAG) versus cyclosporine modified (CsA), have not defined which agent is more cost-effective for immunosuppression in renal transplant recipients especially in a quadruple immunosuppressive regimen. Methods. The objective of this randomized, prospective study was to compare the clinical and economic outcomes of TAC versus CsA, in a regimen that consisted of Thymoglobulin induction, an antimetabolite, and prednisone. Between December 2000 and October 2002, 200 patients were enrolled and randomized in a 2:1 fashion (TAC n=134, CsA n=66). Results. At 1 year, acute rejection (4% TAC vs. 6% CsA), patient survival (TAC 99% vs. CsA 100%), and graft survival (95% TAC versus 100% CsA, P=0.059) were similar. Serum creatinine levels were lower in the TAC group compared with the CsA group (1.3 +/- 0.3 vs. 1.6 +/- 0.7 mg/dL, P=0.03). The incidence of CMV infection was similar between the groups and two patients, both in the TAC arm, developed malignancy. Anti-hypertensive requirement (32% TAC vs. 32% CsA) and the incidence of posttransplant diabetes mellitus (4% TAC vs. 2% CsA) were similar. Pretransplant, fewer TAC patients received dyslipidemia treatment (40% TAC vs. 67% CsA, P=0.0005), while more CsA patients were able to discontinue these medications posttransplant (absolute change 25% TAC vs. 47% CsA). Total 12-month medication costs were similar ($17,723 +/- 11,647 TAC vs. $16,515 +/- 10,189 CsA). Conclusions. When combined with Thymoglobulin induction, an antimetabolite, and corticosteroids, TAC and CsA are comparable in safety, efficacy, and cost in renal transplantation.