Background Dosage quantities of tacrolimus (TAC) vary according to cytochrome P450 3A5 (CYP3A5) genotype. Genotyping is expected to optimize the response to TAC response and to minimize adverse effects. In Thailand, kidney transplantation is reimbursable with the same diagnosis-related group payment regardless of patient's CYP3A5 genotype. Objective This study aimed to determine the costs of TAC administration, therapeutic drug monitoring (TDM), and hospitalization for kidney transplantation across CYP3A5*1/*1, *1/*3, and *3/*3 genotypes. Setting A single transplant center in a university hospital. Method This is an observational study that collected data from patients pooled from both arms of a randomized controlled trial that tested initial doses of TAC. Main outcome measure TAC and TDM cost and hospitalization cost for transplantation were compared between genotypes. Results The CYP3A5*1/*1 patients had the highest median combined TAC-TDM cost and hospitalization cost ($1062 and $9097), followed by CYP3A5*1/*3 ($859 and $6467) and CYP3A5*3/*3 patients ($761 and $5604). The CYP3A5*1/*1 patients had a higher hospitalization cost by $2787 over the CYP3A5*1/*3 patients, despite marginal significance. The CYP3A5*1/*1 patients had a significantly higher cost of TAC plus TDM (by $309) and hospitalization cost (by $3275) than the CYP3A5*3/*3 patients. Both study costs were significantly higher in patients with delayed graft functioning than in patients with instant or slow graft functioning. Conclusion The benefits of genotype detection in patients with CYP3A5*1/*1 should be considered for a higher reimbursement rate because of the substantial differences in total hospitalization cost for kidney transplantation among patients with different CYP3A5 genotypes.