Over the past two decades, public health research has demonstrated that Adverse Childhood Experiences (ACEs) are associated with significant and prolonged physical and mental health problems, demanding investigation into the factors that may mitigate the poor outcomes. One potential factor that may attenuate the negative impact of ACEs on individuals' health is social support. An important source of social support, both during and after adverse childhood experiences, is sibling relationships. Consequently, the purpose of the current study was to examine if two components of sibling relationships-perceived warmth and conflict-affect the relationship between ACEs and wellbeing in adulthood. A total of 439 participants ( M age = 35.06, SD = 11.19) completed self-report measures of their ACEs, their perceived warmth and conflict with a living sibling, and their wellbeing. Results revealed that sibling relationships characterized by higher perceived warmth-and, interestingly, higher perceived conflict-attenuated the negative impact of ACEs on wellbeing in adulthood. Findings from the current study provide valuable information about how psychologist, social workers, and other health professionals may use siblings as a source of social support to mitigate the negative effects of ACEs on wellbeing in adulthood.