Infants with insecure attachment styles are at risk of developing psychopathic behaviors inadolescence and adulthood. In this study, we test the infant attachment styles measured with the Strange Situation Procedure as a predictor of youth psychopathic behaviors measured in three dimensions: remorselessness, unemotionality, and callousness, among 1,149 families in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (SECCYD). Propensity scores for the four attachment groups were estimated with iterative tree-based regression models. After accounting for the potential confounding effects of demographic characteristics and child temperament with the inverse probability of treatment weighting, weighted generalized linear models revealed the association between insecure/avoidant attachment style measured at one year after childbirth and higher levels of remorselessness, unemotionality, and callousness at 15 years. These findings provide insights into the long-term outcomes for attachment relationships established in early life.