This study investigated whether different clusters of patients with personality disorders in a psychoanalytic hospitalization-based treatment were associated with: (a) different changes in personality organization (PO); (b) different pre-treatment variables; and (c) different associations between changes in PO and outcome. K-means clustering analysis identified two clusters of patients, which showed different changes in PO and mainly differed in terms of levels of anaclitic and introjective personality features, respectively. Both clusters showed a significant decrease in symptoms and an improvement in personality functioning during treatment and at 3-month follow-up. Clinical implications of these findings are discussed. Copyright (C) 2010 John Wiley & Sons, Ltd.