Personality disorders (PD) and substance use disorders (SUD) are highly comorbid conditions. However, their treatment services are often separated. The aims of this study was to investigate how extensive this separation was prior to a Norwegian health reform (2004) that promoted integration, and to discuss clinical challenges for an integrated treatment of PD and SUD. All patients with a diagnosis of PD (n=1783) admitted to 10 day hospital treatment programs (1993-2003) were examined. Diagnoses were assessed by Mini International Neuropsychiatric Interview and Structured Clinical Interview for DSM-IV interviews. Socio-demographic data, psychosocial functioning (Global Assessment of Functioning Scale), symptom distress (Symptom Check List-90-Revised), interpersonal problems (Circumplex of Interpersonal Problems) and treatment course were recorded. The majority of patients were females (72%) and the prevalence of SUD was low (14%). SUD occurred among all PD categories. Patients with borderline PD were over-represented and patients with cluster C disorders were under-represented in the SUD sample. The SUD sample contained more men and it was associated with more previous violence against self and others. The reported violence was partly explained by gender (males) and diagnoses (borderline and SUD). PD patients with SUD also displayed more aggression during treatment and dropped out more frequently. The findings demonstrate that the female dominated specialized psychiatric treatment services for PD to a large extent had excluded PD patients who also had SUD. The reasons are probably related to the surplus problems that characterized the SUD sample and gender issues. Implications for the development of the PD and SUD services with respect to an integrated treatment for these comorbid conditions are discussed.