Population pharmacokinetic parameters of vancomycin (VCM) in Japanese adult patients infected with methicillin-resistant Staphylococcus aureus (MRSA) were estimated using 1253 items of serum concentration data from 190 patients obtained in routine drug monitoring. The two-compartment linear model was adopted, and VCM clearance (CL) was correlated with the creatinine clearance (CLcr), which was observed or estimated by the Cockcroft-Gault equation. The population pharmacokinetic analysis program NONMEM with first-order conditional estimation method was used. The results showed VCM clearance to be linearly correlated with CLcr (CL[ml/min] = 0.797 × CLcr) when the estimated CLcr was<85 ml/min, but no linear relationship at higher than this level because of the lack of accuracy in the CLcr estimates. The interindividual variability of CL was 38.5%; K12 and K21 were 0.525 hr-1 and 0.213 hr-1, respectively. The distribution volume at steady state (Vss) was 60.7 1, with no significant dependence on the actual body weight. The interindividual variability of Vss was 25.4%. The calculated half-life (t1/2,β) in a typical patient with CLcr of 85 ml/minute was 12.8 hours. Residual variability was 23.7%. These results were compared to those of healthy volunteers, and guidelines for dosage adjustment in VCM therapy are discussed.