Background: While various factors contributing to delinquency have been explored, the role of self-esteem in this specific context has received little attention. Hence, this study aims to investigate the complex issue of adolescent delinquency in Iran by focusing on the mediating role of self-esteem in the relationship between parental attachment and delinquent behavior. Methods: Using the multistage cluster random sampling method, the research involved 528 high school students in Tehran. Each student completed validated scales assessing their parental attachment, self-esteem, and delinquency at school. Multiple regression analyses with the Sobel test and bootstrapping method were used to examine mediated effects. Results: The findings reveal that self-esteem significantly mediates the relationship between maternal attachment and delinquency (standardized coefficient = −0.0292; p = 0.04). Adolescents with secure maternal attachments tend to exhibit higher self-esteem, which reduces the likelihood of delinquent behavior. In contrast, paternal attachment did not show a significant mediating effect in this study. These results underscore the importance of cultivating secure maternal relationships and fostering positive self-esteem to address adolescent delinquency. Conclusion: The study suggests that targeted interventions that strengthen maternal attachment and boost self-esteem could effectively mitigate delinquent behaviors among Iranian adolescents. These interventions should prioritize the emotional support and value of secure maternal bonds as key factors in promoting healthy adolescent development.