<p>The objective of this study was to evaluate the feasibility and rationale of a six-month Evolutionary Systems Therapy for personality pathology. In doing so, we employed a conceptualization that is supposed to be consistent with dimensional models of personality disorders and evolutionary psychopathology. Twenty-one patients were recruited and stratified into three homogeneous subgroups in accordance with spectra of psychopathology (internalizing, externalizing, schizotypy). An evolutionarily informed conceptualization was shared with patients based on three interpersonal styles that we consider to be prominent in the three spectra. Feasibility indicators were evaluated monthly, while changes in clinical measures were assessed by three procedures: ecological momentary assessment, monthly self-report measures, pre-post self-reports and interviews. At the end of treatment eighteen out of 21 patients were in remission, and all indicators suggested a high feasibility. At group level, a repeated-measures ANOVA reported large effect sizes (η² ranging between .892 to .979) for the whole sample. At individual level, all patients showed reliable changes in measures of personality functioning, maladaptive personality traits, general psychopathology, plus a few common and specific factors (working alliance, self-soothing, self-reflectivity). Ecological momentary assessment suggests that the three interpersonal styles were prominent in the corresponding spectra both before and after the treatment. Despite the limited sample size, the findings are consistent with the importance of a dimensional approach to psychopathology and of an evolutionarily informed conceptualization of personality disorders. This study supports the need for a confirmatory randomized controlled trial on the clinical utility of Evolutionary Systems Therapy.</p>