Non-suicidal self-injury (NSSI) often occurs before age 15, yet the majority of research on risk factors for this dangerous behavior has focused on samples of older participants. Insecure attachment has been previously identified as a risk factor for both NSSI and behavioral problems, and behavioral problems appear to be particularly associated with NSSI among young populations. Redressing the lack of young adolescent NSSI research, the present study uses longitudinal data from a sample of young adolescents to test a model in which insecure attachment acts as a prospective risk factor for NSSI via emotional and behavioral problems. Data on NSSI, child-mother attachment, and emotional and behavioral problems were collected from 559 (41.1% male) Flemish adolescents when they were 13 years old (M = 12.71, SD =0.32), and again 1 year later. Insecure attachment was measured using maternal items on the Experiences in Close Relationships—Revised Child scale. Psychological adjustment was assessed with the Strengths and Difficulties Questionnaire. We found that anxious and avoidant attachment were indirectly associated with NSSI through behavioral problems but not through emotional problems. Findings highlight the role of behavioral problems as a risk factor for NSSI in early adolescence, a rarely studied developmental period during which NSSI often first starts. Findings suggest that one possible pathway for the attachment-NSSI association among young adolescents is through behavioral problems. Therapies that improve child-parent attachment may reduce NSSI among young adolescents both directly, and indirectly by improving behavioral problems.