Non-suicidal self-injury (NSSI) is a serious public health concern that typically onsets during early adolescence. Adolescents (N = 980, ages 12-19 years) admitted for acute, residential psychiatric treatment completed baseline clinical interviews assessing mental disorders and questionnaires measuring demographics, early life adversity, and symptom severity. Prevalence rates of NSSI for lifetime (thoughts: 78%; behaviors: 72%), past year (thoughts: 74%; behaviors: 65%), and past month (thoughts: 68%; behaviors: 51%) were high. Although effect sizes were modest, the presence of a lifetime depressive disorder, sexual abuse, and comorbidity (i.e., three or more current disorders) were significant correlates of experiencing NSSI thoughts and behaviors. Furthermore, lifetime depressive disorder, current anxiety disorder, and comorbidity were associated with a greater odds of persistent NSSI thoughts and/or behaviors. Longitudinal studies are needed to determine whether targeting these factors reduces the persistence of NSSI thoughts and behaviors.