Background: The full version of the Borderline Symptom List (BSL; for clarification now labeled BSL-95) is a self-rating instrument for specific assessment of borderline-typical symptomatology. The BSL-95 items are based on criteria of the DSM-IV, the revised version of the Diagnostic Interview for Borderline Personality Disorder, and the opinions of both clinical experts and borderline patients. The BSL-95 includes 95 items. In order to reduce patient burden and assessment time, a short version with 23 items (BSL-23) was developed. Methods: The development of the BSL-23 was based on a sample of 379 borderline patients, considering the items from the BSL-95 that had the highest levels of sensitivity to change and the highest ability to discriminate borderline patients from other patient groups. In a second step, the psychometric properties of the BSL-23 were investigated and compared with the psychometric properties of the BSL-95 in 5 different samples, including a total of 659 borderline patients. Results: In all of the samples, a high correlation of the sum score was found between the BSL-23 and the BSL-95 (range: 0.958–0.963). The internal consistency was high for both versions (BSL-23/Cronbach’s α: 0.935–0.969; BSL-95/Cronbach’s α: 0.977–0.978). Both BSL-23 and BSL-95 clearly discriminated borderline personality disorder patients from patients with an axis I diagnosis (mean effect sizes were 1.13 and 0.96 for the BSL-23 and BSL-95, respectively). In addition, comparisons before and after 3 months of dialectical behavior therapy revealed a numerically larger effect size for the BSL-23 (d = 0.47) compared to the BSL-95 (d = 0.38). Conclusion: The results indicate that the BSL-23 is an efficient and convenient self-rating instrument that displays good psychometric properties comparable to those of the BSL-95. The BSL-23 also demonstrated sensitivity to the effects of therapy.