The presence of a mental disorder in the mother is one of the key factors affecting attachment. The present study aimed to evaluate prenatal and postnatal attachment among mothers diagnosed with a mental health disorder by comparing them to a healthy group. The patient group included women who received follow-up care in a psychiatric clinic (74 pregnant and 75 postpartum), and the healthy group consisted of women who attended a follow-up polyclinic (118 pregnant and 82 postpartum). Data were collected using questionnaire forms, including the Prenatal Attachment Inventory and the Maternal Attachment Scale. Mothers diagnosed with a mental health disorder were determined to have lower attachment scores than the healthy group, both during the prenatal and postnatal periods. The literature suggests that mothers diagnosed with a mental health disorder showed low maternal attachment scores during pregnancy and/or the postnatal period. Psychiatric nurses should be involved in initiatives that may increase the prenatal and maternal attachment.