The quality of object relations affects interpersonal behaviour, but it is not known whether it modifies effectiveness on personality functioning in psychotherapies of different mode and length. In this study we estimated the modifying effect of the quality of object relations on the effect of solution-focused therapy (SFT) and shortand long-term psychodynamic psychotherapy (SPP and LPP) on self-concept. A total of 326 patients were assessed at baseline with the Quality of Object Relations Scale (QORS) and 4 times during a 3-year follow-up with the Structural Analysis of Social Behavior self-concept questionnaire, comprising altogether 10 scores on different aspects of self-concept pathology. The effectiveness of SFT, but not SPP, was significantly poorer in several domains (5/10) of self-concept for patients with low QORS, i.e. those with less mature relational patterns, than for patients with high QORS, while the reversal occurred in some (3/10) self-concept domains in LPP. The results suggest that the quality of object relations has significance for treatment selection in therapies with different mode and length.