Calculated creatinine clearance (CrCL) estimates are frequently used as estimates of aminoglycoside clearance (AGCL), despite being inadequately studied. Thirty surgical intensive care unit (SICU) patients with stable serum creatinines (0.6–6.3 mg/dl) and steady-state aminoglycoside levels were studied. A one-compartment pharmacokinetic infusion model was used to calculatekandVd; AGCL = (k) (Vd). CrCLs using the equations of Cockroft-Gault (CGCL), Jelliffe (JCL), and Jelliffe uncorrected for body surface area (JCLu) were calculated, then compared to the AGCL. The JCLuwas a better fit to the data (y= 0.98x+ 0.44,r= 0.91) with a superior regression correlation (p< 0.02) than CGCL (y= 0.91x+ 6.07,R= 0.89) and JCL (y= 1.11x+ 2.11,R= 0.89) correlations. CGCL overpredicted the AGCL whereas JCL and JCLuunderpredicted the AGCL. All three methods showed a precision of approximately 20 ml/min. Relative bias and precision show JCLubetter than JCL, CGCL better than JCL only for bias, and CGCL and JCLunot different. The absolute percentage error of the CrCL estimates tended to be lower at higher AGCL and did not differ for CGCL, JCL, and JCLu. In the SICU setting, we suggest the use of the JCLufor estimating the AGCL.