This article presents early findings on the causal effects of a housing voucher on family stress, which plays an important role in children's healthy development. Using the Housing and Children's Healthy Development study, which is the only randomized controlled trial of housing vouchers (conducted in the Cleveland, Ohio, and Dallas, Texas, metropolitan areas), we found measurable health and related benefits accruing to families who received vouchers even though half of those who leased housing with vouchers only lived in that dwelling for roughly one year or less. Vouchers also substantially improved cost burdens, sufficiency of space, adequacy of heat, and daytime neighborhood safety. Our analysis shows that the affordability secured by the voucher (reduction of cost burden) played the most important role in reducing parent stress. One policy implication of the affordability findings is the need to keep families' housing cost burden affordable.