This study examined the pharmacokinetics and dosing requirements of vancomycin in adult liver transplant recipients and also evaluated the predictability of determining vancomycin-dosing requirements utilizing an estimated creatinine clearance (CrCl) approach. Twenty adult liver transplant recipients were included in this analysis. Vancomycin pharmacokinetic parameters and dosing requirements calculated from estimated CrCl and population-based pharmacokinetic equations were compared with values calculated using serum concentrations and assuming a one-compartment model. Compared with the values obtained using equations to estimate the CrCl and vancomycin pharmacokinetics (t, Cl, and Vd), the actual values were statistically different for half-life and clearance (11.0 vs. 16.4 hours and 52 vs. 36 mL/min, respectively; P < 0.01). Additionally, CrCl that were estimated using population-based formulas significantly overestimated actual CrCl calculated using 24-hour urine collections (65-78 vs. 43 mL/min; P < 0.05). The results from this study indicate that serum creatinine concentrations do not adequately predict glomerular filtration rates (GFR) or vancomycin clearance in adult liver transplant recipients. Based on these results, the use of 24-hour urine CrCl to predict GFR and serum concentrations to properly dose vancomycin is advocated.