['Controversy exists about whether insulin resistance (IR) affects response to treatment of hepatitis C. We evaluated the effect of IR on sustained virologic response (SVR) in HIV/hepatitis C virus (HCV)-coinfected patients treated with interferon plus ribavirin.', 'We reviewed the clinical records of HIV/HCV-coinfected patients who received interferon plus ribavirin at our institution between July 2000 and March 2007. IR was defined as a homeostasis model assessment ≥ 3.8. SVR was defined as an undetectable HCV RNA at 24 weeks after the end of treatment. Efficacy was evaluated using an on-treatment (OT) analysis. Multivariate logistic regression analysis was used to evaluate factors associated with SVR.', 'During the study period, 218 patients were treated with interferon plus ribavirin; IR at baseline was available for 162 patients, and 134 were included in the OT analysis; HCV genotype (G) 1/4, 67%; F3-F4 fibrosis, 36%; IR 31%. SVR was achieved in 67 patients (50%) (79% in G 2/3 vs. 38% in G 1/4). IR was associated with a lower SVR [odds ratio (OR), 0.33; 95% confidence interval (CI): 0.15-0.72; P = 0.006). The independent variables related to SVR were genotype 2/3 (OR, 6.7; 95% CI: 2.71-16.98; P < 0.001), absence of IR at baseline (OR, 3.3; 95% CI: 1.36-8.26; P = 0.008), and nadir CD4 T-cell count (OR, 1.002; 95% CI: 1.00-1.00; P = 0.047).'] Does insulin resistance impair response to interferon plus ribavirin in patients coinfected with HIV and hepatitis C virus?