Copyright © by the Southern Society for Clinical Investigation. Introduction: We performed a pilot study examining the safety and tolerability of valacyclovir in veterans with herpes simplex virus type 2 and hepatitis C virus (HCV) coinfection. Methods: We performed a randomized double-blind, placebo-controlled, crossover clinical trial in U.S. veterans with genotype 1 HCV/herpes simplex virus type 2 coinfection. Patients were randomized 1:1 in blocks of 10 to receive either 1 g twice-daily valacyclovir or matching placebo for 8 weeks followed by a 2-week washout phase with daily placebo. The alternate therapy (valacyclovir or placebo) was given for an additional 8-week period. Safety assessments were performed every 2 weeks. Changes in HCV RNA and alanine aminotransferase (ALT) were estimated using linear mixed models (SAS Proc Mixed). Results: Thirty patients were enrolled. Valacyclovir was not associated with toxicity or adverse events. ALT levels declined 6% to 10%; mean HCV RNA levels were reduced 24% (1.3 million IU/mL [0.21 log10 IU/mL]) during the valacyclovir phase (P 5 0.08) with no carryover effect observed (P 5 0.21). Conclusions: Valacyclovir 1 g twice daily showed no evidence of hepatotoxicity in U.S. veterans with hepatitis C. A modest reduction in serum levels of ALT and plasma levels of HCV RNA was observed.