Objectives: Childhood trauma is common and associated with mental ill health. While high rates of trauma are observed across individual disorder groups, there is evidence that trauma is associated with an admixture of affective, anxiety, and psychotic symptoms in adults. Given that both early onset of mental disorder and trauma exposure herald poor outcomes, it is important to examine trauma prevalence rates in youth mental health services and to determine whether this trauma-related clustering is present in help-seeking young people. Methods: We used data from the Transitions Study, a longitudinal investigation of young people attending one of four headspace youth mental health services in Melbourne and Sydney, Australia between January 2011 and August 2012. Participants were 775 young people aged 12 to 25 (65.9% female; mean age = 18.3, SD = 3.2). Childhood trauma was assessed using the Childhood Trauma Questionnaire (CTQ). Multinomial regression was used to assess whether reported childhood trauma was more strongly associated with the co-occurrence of depression, anxiety, mania, and psychosis symptoms than with any one in isolation. Results: Approximately 84% of participants reported some form of abuse (emotional: 68%; physical: 32%; sexual: 22%) or neglect (emotional: 65%; physical: 46%) during childhood or adolescence. Exposure to multiple trauma types was common. Childhood trauma was significantly associated with each symptom domain (depression, mania, anxiety and psychosis). Childhood trauma was more strongly associated with the co-occurrence of these symptoms than with any one of these domains in isolation, such that trauma-exposed young people were more likely to experience increased symptom clustering than their non-exposed counterparts. Conclusions: Childhood trauma is pervasive in youth mental health services and associated with a heterogeneous symptom profile that cuts across traditional diagnostic boundaries.