Abstract Background People with psychosis experience disruptions in personal identity that affect positive and negative symptoms, but the complexity of these phenomena needs to be addressed in an in-depth manner. Using the Personal Construct Theory, we examined whether distinct dimensions of personal identity, as measured with the Repertory Grid Technique along with other cognitive factors, might influence psychotic symptomatology. Method Eighty-five outpatients with schizophrenia-spectrum disorders completed a repertory grid, an observed-rated interview of psychotic symptoms, and measures of cognitive insight, depressive symptoms, neurocognition, and theory of mind. Results Structural equation models revealed that interpersonal dichotomous thinking directly affected positive symptoms. Self-discrepancies influenced positive symptoms by mediation of depressive symptoms. Interpersonal cognitive differentiation and interpersonal cognitive richness mediated the impact of self-reflectivity and neurocognitive deficits in negative symptomatology. Conclusions This study is the first of its kind to examine the structure of personal identity in relation to positive and negative symptoms of psychosis. Results suggest interventions targeted to improving interpersonal dichotomous thinking, self-discrepancies, interpersonal cognitive differentiation, and interpersonal cognitive richness may be useful in improving psychotic symptoms.