Background and Objective: Experiences of being bullied are associated with poorer mental health. Previous research shows that transgender youth have more mental health problems and more school violence experiences than cisgender youth. There is, however, limited knowledge on, whether the associations between bullying and mental health differ between gender identity groups. This study aimed to investigate how experiences of school violence are associated with mental health outcomes among different gender identity groups: cisgender girls, cisgender boys, transfeminine youth, and transmasculine youth. Methods: We utilized data from the Finnish School Health Promotion study (N=152 880), conducted in 2021. Information on experiences of being bullied and on five mental health outcomes (self-perceived health, worries about own mood, anxiety disorder, depression symptoms, social anxiety) was collected with self-administered questionnaire. The associations between bullying and mental health outcomes were analyzed with linear and logistic regression. Results: Trans youth had more bullying experiences and poorer mental health than cisgender youth. Transfeminine youth experienced most school violence, and transmasculine youth had most mental health symptoms. In each gender identity group bullying experiences were associated with poorer mental health. Compared to cisgender boys without bullying experiences, odds of poorer mental health were multiple among transfeminine youth and dozens-fold among transmasculine youth with weekly bullying experiences. Conclusions: Our results highlight significant differences in experiences of school violence and in mental health symptoms between the four gender identity groups studied; while transfeminine youth experienced the most school violence, and transmasculine youth had the most mental health symptoms, cisgender boys reported the least of both. Trans youth should not be considered as uniform population group, but heterogeneity exists among the group as well. The results help to identify groups that are particularly vulnerable to the experiences and effects of bullying and violence. This allows for more effective interventions and support.