This article reviews the role of attachment in difficult-to-treat patients. It is suggested that difficulty often arises in the treatment of these patients because of their inadequate understanding of mental functioning in themselves and in others. The capacity to mentalize is seen as a function of early attachment relationships. Vulnerability introduced by insecure attachment is frequently compounded by a history of intense trauma, leading these patients to defensively inhibit their capacity to think about mental states in their abusers, which then generalizes to other attachment relationships. The clinical implications of this model are discussed.