The objective of the study was to establish aminoglycoside clearance (CLagly) estimates that will more accurately predict serum aminoglycoside concentrations in Veterans Affairs (VA) patients with serum creatinine (SCr) levels below 1 mg/dL. In this prospective study, 79 serum aminoglycoside concentrations were obtained from 50 patients with stable renal function. CLagly was calculated using the Cockcroft-Gault creatinine clearance (CLcr) equation with the patients' measured SCr and also with the SCr value adjusted to 1 mg/dL. The Therapeutic Drug Monitoring System pharmacokinetic computer program was used to calculate expected serum aminoglycoside concentrations based on both SCr values. The Sheiner and Beal method of predicting precision and bias was used to analyze the data. In VA patients, adjusting the SCr to 1 mg/dL for patients with SCr values below 1 mg/dL was significantly more precise and less biased than using the measured SCr for predicting serum aminoglycoside concentrations.