The prevalence and course of renal dysfunction in hospitalized patients and the prescribing of renally eliminated drugs in these patients were studied. All adult inpatients at a large teaching hospital who had a serum creatinine concentration assay performed were screened for renal dysfunction (an estimated creatinine clearance of < 40 mL/min). Renally compromised patients were monitored for changes in renal function. The regimens of selected renally eliminated drugs prescribed for these patients were compared with the manufacturers' recommended dosages for patients with renal compromise. Of the 3800 patients screened, 195 (5%) had renal dysfunction; most of these patients were older than 65 years. Although improvements in renal function were noted in 49 (30%) of the 169 patients with renal dysfunction who were not receiving hemodialysis, elderly patients were less likely to show an improvement in renal function. Of the 60 patients with renal dysfunction for whom a renally eliminated drug was prescribed, 27 (45%) were receiving dosages in excess of the manufacturers' recommendations. Changes in creatinine clearance estimates are common in hospitalized patients with renal impairment. Programs designed to alert physicians to potentially excessive dosages of renally eliminated drugs need to be sensitive to these changes.