Although aminoglycosides have been a mainstay of antibiotic therapy in postsurgical infections, certain patients may be at risk for potential aminoglycoside induced toxicities. Aminoglycoside nephrotoxicity is one of the most frequent causes of iatrogenic renal failure. A narrow toxicity to therapeutic ratio, a relatively long serum half-life and concentration in the renal cortex all contribute to renal dysfunction. Patients at greatest risk for aminoglycoside-induced nephrotoxicity include the elderly, patients with pre-existing renal disease and those who are volume depleted. Calculations based on the results of a multicenter study demonstrate that the average additional cost incurred for each patient who had aminoglycoside-related nephrotoxicity was $2,501. Methods are reviewed for prospectively assessing the potential for development of nephrotoxicity to identify patients for whom effective therapeutic substitutes for aminoglycosides should be sought.