Glaser J‐P, Van Os J, Thewissen V, Myin‐Germeys I. Psychotic reactivity in borderline personality disorder. Objective:  To investigate the stress relatedness and paranoia specificity of psychosis in borderline personality disorder (BPD). Method:  Fifty‐six borderline patients, 38 patients with cluster C personality disorder, 81 patients with psychotic disorder and 49 healthy controls were studied with the experience sampling method (a structured diary technique) to assess: i) appraised subjective stress and ii) intensity of psychotic experiences. Results:  All patient groups experienced significantly more increases in psychotic experiences in relation to daily life stress than healthy controls, borderline patients displaying the strongest reactivity. Borderline patients, moreover, reported significantly more hallucinatory reactivity than healthy controls and subjects with cluster C personality disorder. Paranoid reactivity to daily life stress did not differ between the patient groups. Conclusion:  These results are the first to ecologically validate stress‐related psychosis in BPD. However, psychotic reactivity was not limited to expression of paranoia but involved a broader range of psychotic experiences including hallucinations.