Psychotherapy is the most preferable intervention for personality disorder patients and group psychotherapy offers the possibility to increase the self-perception through resonance and mirroring processes. When a group is disorganized and emotionally tensioned generates regressive movements, which make it a basic assumption group.

To highlight the change of a group of patients after the inclusion of a new patient named Margherita.

The patients were included within the group run by two psychotherapists after a cluster B personality disorder's clinical diagnosis (except for antisocial personality disorder), confirmed by SCID II and by a set of individual interviews aimed to prepare the patient to the inclusion within the group.

Margherita, from the first sessions, showed the tendency to coercively polarize the attention on herself through themes of discouragement and helplessness, posing a threat for the members’ identity and resulting in a disorganization of the work group, which became a basic assumption group.

The temporary disorganization of the group with the consequent regression to a worse functioning condition has subsequently allowed to revitalize the group and to avoid its dissolution. After the temporary regression, indeed, the work group was restored and started again to function even based on the new patient's problems.

The authors have not supplied their declaration of competing interest.