We proposed that having mutually hostile interactions with others is a strong environmental stress factor that, together with diverse psychosocial problems, characterizes adolescents who self-harm. Using cluster analysis, this study examined the naturally occurring patterns of hostility conditions and psychosocial difficulties in a normative sample of 2,029 adolescents (50% boys; Mage = 13.89). Results showed that self-harming behavior was significantly higher among the subgroup of adolescents with mutually hostile interactions who exhibited both internalizing and externalizing problems than among adolescents with other interpersonal–psychosocial configurations. Also, this subgroup of adolescents reported high impulsivity, anger dysregulation, and low self-esteem. These findings support recent research that indicates that adolescents who self-harm also tend to expose others to hostility and display externalizing symptoms.