This retrospective case-control study compared the tolerability and efficacy of linezolid between patients with and without renal insufficiency (serum creatinine > or =1.3 mg/dL for women and > or =1.5mg/ dL for men). All patients with Gram-positive infections treated with linezolid for more than 7 days were included. Data were collected from medical charts and differences between patients with and without renal insufficiency were analysed. Sixty-two patients (40 men), with a mean age of 56.9 years, were enrolled in this study. At the start of linezolid treatment, 17 patients (27.4%) had impaired renal function. Patients with renal insufficiency had a higher prevalence of diabetes mellitus compared with those with normal renal function (64 .7% vs. 22.2%; P=0.002). At the start of therapy, patients with renal impairment had a higher frequency of elevated blood urea nitrogen (51.0+/-21.1mg/dL vs. 18.3+/-9.7mg/dL; P