The present study focuses on selected symptom criteria to distinguish between attention deficit/hyperactivity disorder (ADHD) in adults and borderline personality disorder (BPD). A sample of n = 158 subjects was examined, consisting of BPD patients (n = 37), ADHD patients (n = 58), comorbid BPD/ADHD patients (n = 19), a clinical group of patients fulfilling the diagnostic criteria of a depressive disorder (DEP; n = 22) and a non-clinical control group (KG; n = 22). Selected symptom criteria were investigated by using the German scales "Skala zur Erfassung der Impulsivität und emotionalen Dysregulation der Borderline-Persönlichkeitsstörung" (IES-27), "ADHS-Screening für Erwachsene" (ADHS-LE), "Fragebogen zu dissoziativen Symptomen" (FDS) and a scale for the assessment of paranoid and dichotomous thinking (PADI). Multivariate analyses of variance revealed that BPD patients differed significantly with respect to self-mutilating behaviour, suicidality, dissociation, paranoia and dichotomy from all other groups. The same effect was found for affect regulation. Furthermore BPD patients differed significantly from ADHD patients by a more severe impulsiveness (IES-27), but not through disturbed impulse control and disinhibition overall. Regarding mean differences between ADHD and BPD patients for attentional control, ADHD patients revealed higher scores which just missed significance. For hyperactivity no significant group differences were found which is assumed to be influenced by symptom overlap like restlessness and aversive tension. The findings suggest that BPD-specific criteria, a stronger affective dysregulation and a higher tendency for autoaggressive impulsive reactions are more selective for differential diagnosis than the core symptoms of adult ADHD. Only attentional control might be a useful criterion for differential diagnosis, which should be examined in future studies.