This work reports a preliminary validation of the Peer Conflict Scale (PCS) for Portuguese young adults (ages 18-30 years). This instrument assesses aggression considering two of its forms (overt and relational aggression) and its two functions (reactive and proactive aggression). The initially proposed 4-factor model provided the best fit for our data and was partially invariant by sex. All subscales revealed good reliability based on internal consistency and test-retest indicators. Construct validity was obtained through the investigation of sex differences that align with previous findings on aggressive behavior and in relation to emotion regulation strategies. These initial results suggest that the PCS, originally designed for adolescents, is a promising tool to assess aggression in young adults, notwithstanding the need of additional psychometric studies to further establish the quality of this instrument.