Chronic hepatitis C is frequent and aggressive in HIV-positive patients. Identification of early predictors of response to anti-HCV therapy is needed for a lower rate of response and higher discontinuations, compared to HCV mono-infected subjects. The aim of our study was to evaluate the predictive value of virological response (VR) at week 4-8-12 of Pegylated interferon alpha-2b (PEG-IFN) plus ribavirin (RBV) on sustained virological response (SVR) in HIV-HCV co-infected patients. 100 patients were treated with PEG-IFN (1.5 mcg/Kg/w) plus RBV ( > /=10.6 mg/kg/d) and randomized for 24-48 or 48-72 weeks, respectively for genotype 2-3 and 1-4, in case of response (HCV-RNA PCR negativity) at the end of standard therapy (24 weeks for genotype 2-3, 48 weeks for genotype 1-4). Transcription-Mediated Amplification (TMA) assay for HCV-RNA was also applied. 27 patients reached end-of-treatment response (9 genotype 1-4, 18 genotype 2-3), 21 achieved SVR (8 genotype 1-4, 13 genotype 2-3). 35 patients dropped, 15 due to side-effects. SVR was statistically related to lower baseline HCV-RNA and to VR at week 4-8-12, with PPV 64%, 53% and 58%, and NPV 81%, 96% and 88%, respectively. In 27 patients, TMA was performed and confirmed standard PCR, except in two cases of relapse, who were PCR negative but TMA positive at week-12. In conclusion, VR at week 8 showed the highest NPV on SVR (96%). The study of viral kinetics requires further investigations in HIV-positive patients to guarantee a cost-effective therapy and to guide individually the duration of treatment. In this setting, TMA might be useful.