OBJECTIVE: The impact of baseline CD4 status on hepatitis C virus (HCV) treatment response among patients with HIV/HCV coinfection was investigated using data from a randomized study of peginterferon alfa-2a (40KD) + ribavirin (Peg-IFN/RBV). METHODS: Of 860 patients treated with conventional interferon alfa-2a + ribavirin (IFN/RBV), peginterferon alfa-2a (40KD) + placebo (Peg-IFN), or Peg-IFN/RBV for 48 weeks, 857 patients had baseline CD4 data available and were included in the analysis. Efficacy and safety were analyzed according to baseline CD4 status as absolute cell count and proportion of total lymphocytes. RESULTS: Sustained virologic response (SVR) rates were highest with Peg-IFN/RBV across all CD4 strata. With Peg-IFN/RBV, SVR rates were independent of baseline CD4 in genotype 2/3 patients, but in genotype 1 patients, they tended to be higher with higher CD4 or CD4%. Frequencies of adverse events (AEs) and serious AEs were similar among treatment arms and CD4 strata. Withdrawal and dose reduction rates attributable to safety were highest with CD4 <200 cells/muL. CONCLUSIONS: Peg-IFN/RBV could be effective and well tolerated in HIV/HCV-coinfected individuals with stable HIV. With Peg-IFN/RBV, response tended to increase with higher CD4 counts in genotype 1; however, because of the paucity of patients with CD4 <200 cells/muL, these data require corroboration.