The cost-benefit ratio of tetravalent rhesus rotavirus vaccine (RRV-TV) in Finland for prevention of rotavirus gastroenteritis was assessed in a randomized, double-blind, placebo-controlled trial. Costs related to vaccination, side effects, and gastroenteritis were identified. Children received RRV-TV (n = 1,191) or placebo (n = 1,207) at 2, 3, and 5 months of age with other infant vaccinations. Prospective follow-up averaged 1.0 years per child. An intention-to-treat analysis was performed from the perspective of society. Nine cases of severe rotavirus gastroenteritis occurred in the RRV-TV group, versus 100 in the placebo group (P < .0001); mean cost per vaccinated child was 4 Finnish marks (FIM) in the RRV-TV group, versus 203 FIM in the placebo group. Side effects with related costs occurred after 11% and 7% of doses in the RRV-TV group and placebo group, respectively (P < .001); mean cost per child was 89 FIM vs. 75 FIM. The break-even cost (i.e., net benefit, excluding cost of vaccine) of RRV-TV in prevention of severe rotavirus gastroenteritis was 109 FIM (U.S. $19.60) per child.