Adolescent boys (N = 128) from a maximum security prison for juvenile offenders were administered a task to assess hostile attributional biases. As hypothesized, these biases were positively correlated with undersocialized aggressive conduct disorder (as indicated by high scores on standardized scales and by psychiatric diagnoses), with reactive-aggressive behavior, and with the number of interpersonally violent crimes committed. Hostile attributional biases were found not to relate to nonviolent crimes or to socialized aggressive behavior disorder. These findings held even when race and estimates of intelligence and socioeconomic status were controlled. These findings suggest that within a population of juvenile offenders, attributional biases are implicated specifically in interpersonal reactive aggression that involves anger and not in socialized delinquency.