Dialectical Behavior Therapy (DBT) has long been successfully applied to such behaviors such as nonsuicidal self-injury (NSSI) and more recently, bulimic behaviors. However, it is less clear how patients experiencing these comorbid symptoms may benefit from this treatment modality. Self-criticism, defined as a highly negative attitude towards the self, has been implicated in both EDs and NSSI and is amenable to DBT; thus, further examination of this construct may be beneficial in informing DBT treatment approaches. However, research has only examined these relationships cross-sectionally and no published research has examined self-criticism as a longitudinal predictor of NSSI and ED symptoms. Thus, this study examined self-criticism as a potential driving factor of NSSI in EDs in order to inform treatments, particularly DBT. Data were collected from 92 treatment-seeking adults at ED treatment facilities in the United States. Participants self-reported ED pathology, NSSI engagement, and self-criticism at baseline and a two-month follow-up. A path analysis revealed that self-criticism at baseline was associated with NSSI frequency at follow-up over and above baseline NSSI and ED symptomology. Self-criticism at baseline was not associated with ED pathology at follow-up. Self-criticism longitudinally predicted NSSI, but not ED pathology, in an ED sample. As such, it may be important for clinicians to assess for self-criticism and consider treatments that target both self-criticism and self-injury, like DBT, for this population.