Medication errors in patients with reduced creatinine clearance are harmful and costly; however, most studies have been conducted in large academic hospitals. As there are few studies regarding this issue in smaller community hospitals, we conducted a multicenter, retrospective cohort study in six community hospitals (100 to 300 beds) to assess the incidence and severity of adverse drug events (ADEs) in patients with reduced creatinine clearance. A chart review was performed on adult patients hospitalized during a 20-month study period with serum creatinine over 1.5 mg/dl who were exposed to drugs that are nephrotoxic or cleared by the kidney. Among 109,641 patients, 17,614 had reduced creatinine clearance, and in a random sample of 900 of these patients, there were 498 potential ADEs and 90 ADEs. Among these ADEs, 91% were preventable, 51% were serious, 44% were significant, and 4.5% were life threatening. Of the potential ADEs, 54% were serious, 44% were significant, 1.6% were life threatening, and 96.6% were not intercepted. All 82 preventable events could have been intercepted by renal dose checking. Our study shows that ADEs were common in patients with impaired kidney function in community hospitals, and many appear potentially preventable with renal dose checking.