Internationally-adopted adolescents who are adopted as young children conditions of poverty and deprivation have poorer physical and mental health outcomes than adolescents conceived, born and raised in the US by families similar to those who adopt internationally. Using a sample of Russian and Eastern European adoptees to control for Caucasian race and US born, non-adopted offspring of well-educated and well-resourced parents to control for post-adoption conditions, we hypothesized that the important differences in environments, conception to adoption, might be reflected in epigenetic patterns between groups, specifically in DNA methylation. Thus, we conducted an epigenome-wide association study (EWAS) to compare DNA methylation profiles at approximately 416,000 individual CpG loci from peripheral blood mononuclear cells of 50 adopted youth and 33 non-adopted youth. Adopted youth averaged 22 months at adoption and both groups averaged 15 years at testing, thus roughly 80% of their lives were lived in similar circumstances. Although concurrent physical health did not differ, cell type composition predicted using the DNA methylation data revealed a striking difference in the white blood cell type composition of the adopted and non-adopted youth. After correcting for cell type and removing invariant probes, 30 CpG sites in 19 genes were more methylated in the adopted group. We also used an exploratory functional analysis that revealed that 223 Gene Ontology (GO) terms, clustered in neural and developmental categories, were significantly enriched between groups.