This paper calculates the cost-benefit ratios for the High/Scope Perry Preschool Program using longitudinal data as the participants reached age 40. Costs were compared to benefits in terms of educational attainment, earnings, and crime reduction. Using a 3% discount rate, the Perry Preschool Program yields a benefit cost ratio of 13 to 1. Using a 7% discount rate, the program yields a benefit-cost ratio of 6 to 1. There are strong differences by gender and a substantial fraction of the total benefits come from reduced crime by male participants.