This article derives an updated cost-benefit ratio for the High/Scope Perry Preschool Program, an intensive preschool intervention delivered during the 1960s to at-risk children in Ypsilanti, Michigan. Because children were randomly assigned to the program or a control group, differences in outcomes are probably attributable to program status. Data on outcome differences is now available on participants as they reached the age of 40; outcomes include educational attainment, earnings, criminal activity, and welfare receipt. These outcomes are rendered in money terms and compared to the costs of delivering the program to calculate the net present value of the program both for participants and for society. The data show strong advantages for the treatment group in terms of higher lifetime earnings and lower criminal activity. For the general public, gains in tax revenues, lower expenditures on criminal justice, lower victim costs, and lower welfare payments easily outweigh program costs. At a 3% discount rate the program repays $12.90 for every $1 invested from the perspective of the general public; with a 7% discount rate, the repayment per dollar is $5.67. Returns are even higher if the total benefits--both public and private--are counted. However, there are strong differences by gender: a large proportion of the gains from the program come from lower criminal activity rates by the treatment group, almost all of which is undertaken by the males in the sample. The implications of these findings for public policy on early childhood education are considered. (Contains 8 tables and 15 notes.)