Recall is an active reconstruction process likely to distort past experiences. This distortion, known as recall bias, seems to manifest itself differently in sick and healthy people. A recall bias has been documented in several disorders, but never investigated in borderline personality disorder (BPD). To determine recall bias in BPD, we assessed momentary and retrospective ratings of specific emotions in 50 patients with BPD and 50 healthy controls (HCs), using the methodology of 24-hour ambulatory monitoring. Our data reveal a group-specific valence-dependent recall bias of retrospective self-report, indicated by a different overall recall pattern in HCs and BPD. BPD patients show an overall negative recall pattern, whereas HCs show a positive recall pattern. A traditional questionnaire approach does not distinguish between symptoms of the disorder and recall bias, although the pathological mechanisms underlying them as well as the appropriate treatment strategies may be different.