This study investigates the relative impact of trauma experiences that occurred prior to and since becoming homeless on depressive symptoms, posttraumatic stress disorder (PTSD) symptoms, and self-injurious behaviors among a sample of homeless youth (N = 389). Youth (aged 13 to 25) who had been homeless or precariously housed in the past year completed a survey about housing history, experiences of violence and victimization, mental health, and service utilization. In addition to examining the impact associated with specific trauma types, we also considered the effect of "early-on" poly-victimization (i.e., cumulative number of reported traumas prior to homelessness) and the influence of a compound sexual trauma variable created to represent earlier complex trauma. This created-variable has values ranging from no reported trauma, single trauma, multiple non-sexual traumas, and multiple traumas that co-occurred with sexual abuse. Multivariate analyses revealed that specific traumatic experiences prior to homelessness, including sexual abuse, emotional abuse/neglect, and adverse home environment, predicted greater mental health symptoms. Poly-victimization did not add to the prediction of mental health symptoms after the inclusion of specific traumas. Results with early compound sexual trauma revealed significant differences between lower-order trauma exposures and multiple-trauma exposures. Specifically, experience of multiple traumas that co-occurred with sexual trauma was significantly more detrimental in predicting PTSD symptoms than multiple traumas of non-sexual nature. Findings support the utility of an alternate/novel conceptualization of complex trauma, and support the need to carefully evaluate complex traumatic experiences that occurred prior to homelessness, which can impact the design and implementation of mental health care and services for homeless youth.