ABSTRACT Low self-concept clarity is associated with self-injurious urges among persons with borderline personality disorder (BPD). Self-critical rumination may potentially exacerbate these associations. Yet empirical research on how self-critical rumination and self-concept clarity interact is scarce. We examined near-term associations between bedtime self-critical rumination, self-concept clarity, and self-injurious urges among adolescents who met at least 3 diagnostic criteria for BPD (N = 22; 63.6% girls/women; M age = 16.45). Participants were sent five daily mobile surveys for 20 days (1691 total assessments completed). Bedtime self-critical rumination moderated concurrent associations between self-concept clarity and self-harm wishes, but not suicide desires. Lower self-concept clarity was associated with elevated self-harm wishes only among participants with moderate to high bedtime self-critical rumination. Findings provide a preliminary step toward understanding the link between self-concept clarity and self-injurious urges.