Using the NONMEM program, the population kinetics of gentamicin were retrospectively studied in a series of 51 patients with different pathologies undergoing treatment (single or three daily doses) with gentamicin whose serum gentamicin levels were being monitored. Renal function, the type of treatment and cancer proved to be the covariates which affected drug clearance, while patient weight was found to govern the distribution volume. The distribution coefficient of gentamicin in the patients was 0.37 litres/kg, justifying gentamicin doses higher than those used conventionally. The optimized population model allowed us to simulate drug serum levels at 8 and 12h, as well as the area under the curve of gentamicin and its variability in patients with high distribution volumes when dosage regimens based on a single daily dose administration are implemented.