Information about the relationship between personality disorder and ethnicity or migration is sparse. The few studies regarding the prevalence of borderline personality disorder (BPD) in immigrants compared to an indigenous population are inconsistent. Castaneda and Franco (1985) found no ethnic group differences in rates of BPD, whereas the study of Pascual et al. (2008) showed that immigrants in a psychiatric emergency service had a lower likelihood of being diagnosed with BPD.The aim of the present study was to compare the frequency of borderline personality disorder in psychiatric inpatients with an immigrant background vs. the indigenous group.A total of 2494 consecutive patients over a three-year period at a psychiatric university hospital were reviewed. Data included socio-demographic and clinical variables and also information about an immigrant background, although no specific data of the provenance of the individual migrant patient were obtainable. The psychiatric diagnosis was limited to information available from the digital documentation system of the psychiatric clinic and additionally from discharge letters. The diagnosis of borderline personality disorder was based on ICD-10 criteria.Of the study population 374 individuals (15%) had an immigrant background. The rates of BPD were 6.5% in the indigenous group (n=2120) vs. 3.5% in the immigrant group (n=374). The difference between the indigenous and the immigrant group regarding the rates of BPD-diagnoses was statistically significant (chi 2 =5,02, df=1, p=0,025).In accordance to the findings of Pascual et al. (2008) and challenging the results of Castaneda and Franco (1985), our findings suggest that in a clinical sample BPD was diagnosed less frequently in the immigrant group than in the indigenous group. Therefore, our results do not support the concept of immigration as a risk factor for BPD.Possible explanations for our finding are a true lower prevalence of BPD amongst the immigrant group, or ethnic variations in the symptomatology of BPD (Selby and Thomas, 2009), or a cross-cultural bias in the diagnostic process. However, future investigations with a prospective study design and at epidemiological levels need to be conducted in order to get more precise information about the true prevalence of BPD in different immigrant groups and to derive an explanation for the apparent discrepancy in prevalence, and the influence of a cross-cultural setting on the diagnostic process.