This paper has arisen out of the understandings gained following the in-patient treatment of a severely disturbed and self-damaging young woman with a borderline personality disorder. The phenomenon of protective identification is considered in terms of its capacity affectively to control apparently separate and independent professional structures within a hospital setting so that an entire institution may become mobilised into reflecting and acting out one patient's internal world. This phenomenon is illustrated using examples from the patient's own art-work and by clinical vignettes which aim to highlight the destructively regressive processes which occurred. One of the greatest difficulties was found to be the seemingly inevitable loss of boundaries between self and object; between intrapsychic and interpersonal; between staff-member and patient. Consequently some thoughts are offered concerning the need for structures, practical and theoretical, which can be utilised to help recognise and understand the enormously complex and diverse events which such a situation so often engenders.