The place of defense mechanisms in assessing personality in psychiatry is reviewed. After the introduction of the concept of defense by Freud, its development suggests an increasing relevance in clinical practice. In spite of the many difficulties in operationalizing defense mechanisms, a considerable amount of research has been carried out in the last decades. This has resulted in more uniform definitions, a hierarchy of defense mechanisms and, recently, in a proposal for the assessment of defense mechanisms in DSM-IV (the Defense Function Scale).
Four methods of assessment (clinical judgement, standardized interviews, projective tests and self-reporting questionnaires) are discussed. It is concluded that interviews yield the most valuable data, whereas self-reporting questionnaires might be useful as screening instruments. The development of the Defense Function Scale of DSM-IV is a stimulus for further research into reliability and validity of assessing defense mechanisms.