Zoledronic acid(ZA)dosage should be adjusted according to the risk it poses for renal impairment. The recommended dosage for patients with creatinine clearance(Ccr)of less than 60mL/min was established on the basis of an area under the curve analysis, but is doubted because it was calculated without performing a clinical trial. Creatinine secretion from the renal tubule affects Ccr; therefore, using Ccr as the basis for dosage adjustment may be inappropriate since this can cause an overestimation of the glomerular filtration rate(GFR). The Japanese Society of Nephrology recommends using the estimated GFR(eGFR)for evaluating renal function. Therefore, this study investigated the relationship between renal function before and adverse events(AEs)after ZA administration. The dosage of only 3 of the 47 patients with Ccr less than 60mL/min could be adjusted on the basis of Ccr. During ZA therapy(3 courses), the blood urea nitrogen level and occurrence of hypokalemia were higher in the non-adjusted group than in the adjusted group, but the total number of AEs was equivalent for both groups. For all the patients, Ccr and eGFR were used as parameters for investigating AEs; the total number of AEs was equivalent for patients with differing levels of renal function. Therefore, we suggest that AEs observed during ZA therapy did not depend on the renal function level before ZA administration.