A meta-analysis of 12 randomized trials (1574 patients) examined herpesvirus and related outcomes following organ transplantation over a range of acyclovir exposures (including valacyclovir). Overall, cytomegalovirus (CMV) infection (odds ratio [OR], 0.44; 95% confidence interval [CI], 0.34-0.57; P<.001), CMV disease (OR, 0.41; 95% CI, 0.31-0.54; P<.001), death (OR, 0.60; 95% CI, 0.40-0.90; P=.01), opportunistic infection (OR, 0.70; 95% CI, 0.53-0.91; P=.009), acute graft rejection (OR, 0.67; 95% CI, 0.52-0.86; P<.001), herpes simplex virus disease (OR, 0.17; 95% CI, 0.12-0.24; P<.001), and varicella-zoster virus disease (OR, 0.06; 95% CI, 0.01-0.25; P<.001) were significantly reduced. Increased acyclovir exposure influenced more end points: Maximum efficacy resulted from valacyclovir (8 g/day). Increasing acyclovir exposure to that achieved with valacyclovir extends benefits of prophylaxis to include impact on graft rejection and opportunistic infections.