Borderline personality disorder (BPD) is associated with many negative physical health outcomes, including increased risk for serious chronic diseases such as diabetes, heart disease, and arthritis. BPD is also linked with obesity, a condition that is strongly related to many of the same physical health problems. Although research has shown that BPD is related to these physical conditions, there is limited evidence of whether body mass mediates the relation between BPD and serious physical health problems. The present study examined the associations among BPD features, body mass index (BMI), and six major physical health problems in an epidemiologically based sample (is = 1051) of Saint Louis residents, ages 55-64. Using interviewer-, self-, and informant-report of personality pathology, we found that BPD features were significantly related to reported presence of heart disease, arthritis, and obesity. BMI was also significantly related to heart disease and arthritis. Sobel mediation models showed that BMI fully mediated the relation between BPD features and arthritis. These results suggest that borderline pathology is an important risk factor for serious health problems in later adulthood. Obesity appears to be one pathway that leads to more health problems among individuals with BPD symptoms and may be a useful starting point when thinking about future intervention strategies.