This study provides estimates of the prevalence and demographic features of borderline personality disorder (BPD) in a community sample as well as BPD comorbidity rates with Axis I and II disorders. In addition, the authors provide data on general functioning and treatment seeking among individuals with BPD. Data from 34,481 participants in the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) were analyzed. Results suggest that 2.7% of adults in the United States meet diagnostic criteria for BPD, with slightly higher rates of the disorder in females, people in lower income brackets, people younger than 30, and individuals who are separated or divorced. Racial/ethnic differences were evident, with Native Americans (5.0%) and Blacks (3.5%) having significantly higher rates of the disorder, on average, and Asians having significantly lower rates (1.2%). Individuals with a BPD diagnosis were likely to have co-occurring lifetime mood disorders, anxiety disorders, substance use disorders, and other personality disorders. Specifically, 84.8% of individuals with BPD also had a lifetime anxiety disorder, 82.7% had a lifetime mood disorder/episode, and 78.2% were diagnosed with a lifetime substance use disorder. Individuals with BPD showed significant impairment in functioning and were highly likely to seek therapy or receive medication for mental health concerns.