Aggression directed at peers can be either overt or relational, with overt aggression including acts such as physical threat or assault and relational aggression including acts such as social exclusion and social ostracism. The current study sought to understand the relationships between overt and relational aggression, social anxiety, loneliness, depressive symptoms, and alcohol and drug use in a sample of 287 undergraduate college students who completed self-report questionnaires on peer aggression, personality factors, substance abuse, and mental health factors. Results of multivariate analysis of variance revealed, unexpectedly, that males engaged in both overt and relational aggression at higher levels than females. Both types of peer aggression were significantly and positively associated with social anxiety, loneliness, depressive symptoms, alcohol use, and drug use. Separate regression analyses for men and women indicated the unique predictive contribution of each type of aggression with each psychosocial adjustment variable. Future research should focus on a longitudinal investigation of the relations between peer aggression and psychosocial adjustment so that directionality can be established. Implications of the findings for school administrations and health professionals are considered. Tables, references