Nonsuicidal self-injury (NSSI) has become a significant public health problem. Although numerous studies have examined cross-sectional psychological correlates of NSSI, there has been little research examining predictors of NSSI over time. The present study examined cross-sectional and longitudinal correlates of NSSI in 81 young adult self-injurers (M age = 19, 74.1% female, 51.9% Caucasian), 51 of whom were followed up 1 year later. At baseline, participants completed self-report measures of NSSI, Axis-I disorders, borderline personality disorder (BPD), and impulsivity, as well as an implicit measure of NSSI attitudes and identity. One year later, participants completed a Timeline Followback Method whereby they indicated their engagement in NSSI over the previous 12 months. Analyses replicated many known cross-sectional correlates of NSSI, including symptoms of several Axis-I disorders and BPD. However, many of these same variables failed to predict the course of NSSI over the 1-year follow-up. The only variables to prospectively predict NSSI were past NSSI (i.e., frequency, methods, and recency of NSSI), participants' behavioral forecast of their engagement in future NSSI, and BPD features. Findings suggest that many cross-sectional correlates of NSSI may not be useful for predicting subsequent NSSI. Instead, NSSI severity and BPD features appear to best predict continued engagement in NSSI. (Contains 3 tables.)