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The average age of patients initiating therapy for HCV is increasing, with older patients exhibiting lower responses to therapy than younger patients. Identification of those older patients likely to respond needs to be addressed. Using data from 569 genotype-1 patients enrolled in two phase III studies (NV15801/NV15942) randomized to peginterferon alfa-2a (40KDa) 180 μg/week plus ribavirin 1000/1200 mg/day for 48-weeks, we investigated factors associated with sustained virological response (SVR; undetectable HCV-RNA 24-weeks post-treatment) in patients >50 years. SVR rates among patients ≤50 was greater than those >50 years (52%vs 39%; P = 0.0073). Older patients with a rapid virological response (RVR; undetectable HCV-RNA at treatment week 4) or complete early virological response (cEVR; detectable HCV-RNA at week 4 but HCV-RNA <50 IU/mL at week-12) demonstrated high SVR rates (83% and 61% respectively). Older patients had lower cumulative peginterferon alfa-2a exposure and significantly lower cumulative ribavirin exposure (252 g vs 304 g in younger patients; P < 0.0001). Higher relapse rates were observed in older patients (41%vs 25%; P = 0.0042). Cumulative drug exposure and achievement of RVR or cEVR were significantly predictive of SVR by multiple logistic regression analysis in patients >50 years. Other baseline characteristics predictive of SVR in those >50 years of age were lower baseline HCV-RNA level (P = 0.0067), higher ALT-ratio (P = 0.0113) and absence of cirrhosis (P = 0.0482). Response rates were high among patients >50 years without cirrhosis who maintained adequate drug exposure and those achieving an RVR or cEVR. More frequent dose modifications of ribavirin in those >50 years likely contributed to the observed higher relapse rates.