The concept of attachment in long-term interpersonal relationships has been linked to relationship outcome and social-emotional health. To date, no relationship between the structural properties of the human amygdala and attachment in romantic relationships (measured through self-reported attachment related anxiety and avoidance) has been described. The aim of the current study was to investigate the relationship between amygdala structure as well as amygdala structural and functional connectivity and attachment anxiety and avoidance. To this end, we collected self-report attachment data on a sample of female young adults. We then examined associations between attachment and mean diffusivity, fractional anisotropy and resting state functional connectivity MRI (rs-FC) of the amygdala and its white matter connections with the prefrontal cortex. We found that lower integrity of the left amygdala was linked with attachment avoidance (e.g., being less comfortable in seeking proximity with others and depending on others) and that greater structural integrity of the uncinate fasciculus was positively associated with avoidance. Lastly, we found that stronger rs-FC between the bilateral amygdala and medial prefrontal regions was linked with greater avoidance. Our findings are compatible with and expand previous results reported by studies that have taken a task-related fMRI approach, furthering our understanding of the neurobiological mechanisms of attachment, and in particular implicating the system formed by amygdala and prefrontal areas in the patterns of behavior that regulate emotional proximity in romantic relationships. These findings have the potential to further our understanding of the affective mechanisms underlying attachment behavior.