Clinical research and public policy reviews that have emerged in the past several years now make it possible to estimate the cost‐benefits of early intervention for infants, toddlers, and preschoolers with autism or pervasive development disorder—not otherwise specified (PDD—NOS). Research indicates that with early, intensive intervention based on the principles of applied behavior analysis, substantial numbers of children with autism or PDD—NOS can attain intellectual, academic, communication, social, and daily living skills within the normal range. Representative costs from Pennsylvania, including costs for educational and adult developmental disability services, are applied in a cost‐benefit model, assuming average participation in early intensive behavioral intervention (EIBI) for three years between the age of 2 years and school entry. The model applied assumes a range of EIBI eAects, with some children ultimately participating in regular education without supports, some in special education, and some in intensive special education. At varying rates of eAectiveness and in constant dollars, this model estimates that cost savings range from $187,000 to $203,000 per child for ages 3‐22 years, and from $656,000 to $1,082,000 per child for ages 3‐55 years. DiAerences in initial costs of $33,000 and $50,000 per year for EIBI have a modest impact on cost‐benefit balance, but are greatly outweighed by estimated savings. The analysis indicates that significant cost-aversion or cost-avoidance may be possible with EIBI. #1998 John Wiley & Sons, Ltd.