This paper estimates the large array of long-run benefits of an influential early childhood program targeted to disadvantaged children and their families. It is evaluated by random assignment and follows participants through their mid-30s. The program is a prototype for numerous interventions currently in place around the world. It has substantial beneficial impacts on (a) health and the quality of life, (b) the labor incomes of participants, (c) crime, (d) education, and (e) the labor income of the mothers of the participants through subsidizing their childcare. There are substantially greater monetized benefits for males. The overall rate of return is a statistically significant 13.0% per annum with an associated benefit/cost ratio of 6.3. These estimates account for the welfare costs of taxation to finance the program. They are robust to a wide variety of sensitivity analyses. Accounting for substitutes to treatment available to families randomized out of treatment shows that boys benefit much less than girls from low quality alternative childcare arrangements.