['To investigate the association between insulin resistance and rapid virologic response.', 'All consecutive HIV/hepatitis C virus coinfected patients who started peg-interferon alpha-2a (180 microg/week) and ribavirin 1000-1200 mg/day were analysed.', 'Insulin resistance was defined according to the homeostasis model of assessment-insulin resistance calculated as fasting insulin (mIU/l) x fasting glucose (mmol/l)/22.5. Rapid virologic response was defined as testing negative for hepatitis C virus-RNA after 4 weeks of therapy. Fasting levels of insulin and glucose in plasma were measured in all patients on the first day of treatment. Hepatitis C virus-RNA was determined by quantitative PCR assay (version 3.0). Hepatitis C virus-RNA was measured by qualitative PCR assay (COBAS 2.0) after 4 weeks of treatment.', 'Seventy-four HIV/hepatitis C virus coinfected patients were enrolled [mean age 41.7 years (SD 5.3), 61 men, 54.1% with advanced fibrosis (F3-4 according to METAVIR classification), 52.4% with infection by hepatitis C virus genotype 1 or 4]. Rapid virologic response was reached by 30 subjects. In the multivariate analysis the independent predictors of rapid virologic response were: genotype 1 or 4 [adjusted odds ratio 0.18 (0.06-0.55)], hepatitis C virus-RNA < 400.000 UI/ml [adjusted odds ratio 0.229 (0.09-0.92)] and homeostasis model of assessment-insulin resistance more than 3.00 [adjusted odds ratio 0.1 (0.05-0.6)].'] Does insulin resistance impair rapid virologic response in HIV/hepatitis C virus coinfected patients on peginterferon-alfa-2a?