Significant links exist between one’s perception of available social support and mental health outcomes, including during the transition to motherhood. Yet, attachment theory posits that individuals do not benefit equally from social support. As such, we examined the influence of attachment representations (i.e., secure base script knowledge) as they potentially moderate links between social support and psychological distress in a 1-year longitudinal study of an ethnically diverse (56% White) sample of infant-mother dyads. We hypothesized that higher social support would predict lower maternal psychological distress and this relation would be strongest in those with higher secure base script knowledge. Results indicated that maternal perceptions of social support were significantly negatively correlated with psychological distress. Analyses revealed that secure base script scores significantly moderated these associations. Interestingly, for those high in script knowledge, low social support predicted greater psychological distress. For those low in script knowledge, social support was unrelated to psychological distress. This pattern suggested that those who expect care (i.e., high secure base script knowledge) but receive minimal support (i.e., low perceived social support) find motherhood uniquely dysregulating. Practitioners may do well to examine individuals’ attachment expectations in relation to their current social support.