Purpose This study evaluated the risk posed by attachment type in the development of anxiety or depression symptomatology in Mexican adults. Design and Methods This was case-control study in which anxiety and depression symptomatology levels were compared according to the attachment type reported by 3,666 participants. Findings It was found that insecure attachment is a risk factor (p≤.001) for the development of severe levels of depression (OR = 2.12, CI 95%: 1.66–2.70) and anxiety symptomatology (OR = 1.52, 95% CI: 1.30–1.77). Findings are discussed based on their implications for psychiatric nursing practice. Practice Implications The findings of this study enable nurses to consider the empirical validity of attachment theory for studying psychosocial aspects of mental health and to design intervention strategies that promote secure attachment in populations without psychiatric diagnoses to prevent anxiety and depression symptomatology.