Personality disorders are an ill-defined group of psychopathological conditions that are increasingly seen as one of the main domains of NHS dynamic psychotherapy. The authors discuss some of the concepts that underlie the diagnosis though it can most easily be understood as severe non-psychotic pathology. Psychoanalytic theory has suggested several paradigms to understand and treat such conditions, and most of these rely on interpretation as the central therapeutic agent. The authors argue in this paper that therapists may need to consider the use of limit setting with patients with personality disorder where dangerous acting out may occur. This runs counter to the principles of therapeutic neutrality, and yet the limit setting may be a prerequisite to an effective therapeutic encounter.