Only a few treatment studies of personality disorders (PD) patients are on longer-term psychotherapy, general outcome measures are used, and follow-up periods are usually short. More studies of long-term therapies, using outcome measures of core psychopathology, are needed.

This study is a dismantling randomized controlled clinical trial, specifically designed to study long-term effects of transference interpretation. Forty-six patients with mainly cluster C personality disorders were randomly assigned to 1 year of dynamic psychotherapy with or without transference interpretations. The outcome measures were remission from PD, improvement in interpersonal functioning, and use of mental health resources in the 3-year period after treatment termination.

After therapy with transference interpretation PD-patients improved significantly more in core psychopathology and interpersonal functioning, the drop-out rate was reduced to zero, and use of health services was reduced to 50%, compared to therapy without this ingredient. Three years after treatment termination, 73% no longer met diagnostic criteria for any PD in the transference group, compared to 44% in the comparison group.

PD-patients with co-morbid disorders improved in both treatment arms in this study. However, transference interpretation improved outcome substantially more. Long-term psychotherapy that includes transference interpretation is an effective treatment for cluster C personality disorders and milder cluster B personality disorders.