Foster youth often experience considerable adversity both in and out of foster care, including histories of abuse and/or neglect, and further stressors within the foster system. These adverse experiences often occur at key developmental periods that can compromise emotional functioning and lead to posttraumatic symptomatology, including posttraumatic stress disorder (PTSD) and emotion dysregulation. In the face of difficult histories and ongoing mental health challenges, youth transitioning into adulthood may be particularly vulnerable to increases in depressive symptoms. We explored the trajectory of depressive symptoms in foster youth from age 17 to 19 using a piecewise linear growth model, examining the effects of PTSD and emotion dysregulation on youth’s depressive symptoms over time. Results revealed depressive symptoms decreased from age 17 to 18 but increased from 18 to 19. PTSD and emotion dysregulation predicted greater baseline depressive symptoms and decreases in symptoms from age 17 to 18, whereas only PTSD predicted increases in depressive symptoms from 18 to 19. Females reported higher levels of depressive symptoms compared to males. Additionally, emotion dysregulation was a stronger predictor of depressive symptoms for females than males. Implications for service delivery for foster youth transitioning into adulthood are discussed.