Introduction: Recent evidence demonstrates an association between social media addiction (SMA) and aggressive behaviors; however, the longitudinal relationship between these two variables remains not fully understood. The aim of this study was to examine the longitudinal relationship between SMA and aggressive behaviors (overt and relational aggression) in early adolescence and to identify gender differences in this relationship. Methods: A sample of 568 Italian early adolescents (52.3% girls; M[subscript age] = 12.59, SD = 0.87) attending middle schools in northern Italy was recruited from different schools. Participants completed an anonymous questionnaire to assess SMA and the perpetration of overt and relational aggressive behaviors. The questionnaire was completed twice with a 1-year intervals (T1 and T2). Results: The findings showed that females were at higher risk of SMA and relational aggression, whereas males exhibited higher levels of overt aggression at both time points (T1 and T2). Longitudinal analyses revealed that SMA at T1 was associated with higher likelihoods of both overt and relational aggression at T2 across both genders and that only in females was relational aggression at T1 associated with higher levels of SMA at T2. Conclusions: The study suggests a relationship between SMA and aggressive behaviors and reveals gender differences in this pattern. Limitations, future directions, and practical implications of the research are discussed.