Background: Some women develop symptoms of posttraumatic stress following childbirth. There is preliminary evidence that cognitive variables may be associated with the development or maintenance of these symptoms. Research indicates that symptoms of posttraumatic stress following childbirth may have negative consequences for mother-infant relationship outcomes. However, these may be attributable to comorbid symptoms of depression. Further evidence is required regarding the nature of the relationships between these variables. Methods: An internet based cross-sectional questionnaire design was employed to test hypothesised relationships between maternal attachment experiences, metacognition, symptoms of PTSD and depression and perceptions of the mother-infant bond, in an analogue sample of new mothers. Structural equation modelling was employed for the principal analysis. Results: The final structural model demonstrated a good fit to sample data. Metacognition fully mediated the relationship between attachment experiences and postnatal psychological outcomes. The association between posttraumatic stress and maternal perceptions of the mother-infant bond was fully mediated by depression. Conclusions: Metacognition may have a key role in the development and maintenance of postnatal psychological distress. If clinically significant postnatal depression is identified, screening for posttraumatic stress is strongly indicated.