This article presents the results of a cost-effectiveness analysis of early intervention services in Massachusetts. The findings indicate that (for a $1,000 investment) children demonstrate different levels of improvement in adaptive behavior and child-mother interaction depending on the severity of their disability and their age of entry into early intervention. Estimates of the number of service hours required to produce maximum gains also varied by outcome measure and child characteristics. Comparisons were made between these estimates and the hours of service received. The implications of these results for policy and future research are discussed.