Data supporting the contraindication of nitrofurantoin for patients with a CrCl less than 60 mL/min are nonexistent. Well-designed clinical trials with urinary concentration information and clinical end points on patients with various degrees of renal impairment are much needed. Until such a study becomes available, the limited data available would support considering using this drug in patients with a CrCl of 40 mL/min or higher.