Many autistic children experience difficulties in their communication and language skills development, with consequences for social development into adulthood, often resulting in challenges over the life-course and high economic impacts for individuals, families, and society. The Preschool Autism Communication Trial (PACT) intervention is effective in terms of improved social communication and some secondary outcomes. A previously published within-trial economic analysis found that results at 13months did not support its cost-effectiveness. We modeled cost-effectiveness over 6years and across four European countries. Using simulation modeling, we built on economic analyses in the original trial, exploring longer-term cost-effectiveness at 6years (in England). We adapted our model to undertake an economic analysis of PACT in Ireland, Italy, and Spain. Data on resource use were taken from the original trial and a more recent Irish observational study. PACT is cost-saving over time from a societal perspective, even though we confirmed that, at 13months post-delivery, PACT is more expensive than usual treatment (across all countries) when given to preschool autistic children. After 6years, we found that PACT has lower costs than usual treatment in terms of unpaid care provided by parents (in all countries). Also, if we consider only out-of-pocket expenses from an Irish study, PACT costs less than usual treatment. PACT may be recommended as a cost-saving early intervention for families with an autistic child.