There have been few longitudinal studies of deliberate self-harm (DSH) in adolescents. This cross-national longitudinal study outlines risk and protective factors for DSH incidence and persistence.Seventh and ninth grade students (average ages 13 and 15 years) were recruited as state-representative cohorts, surveyed, and then followed up 12 months later (N = 3,876), using the same methods in Washington State and Victoria, Australia. The retention rate was 99% in both states at follow-up. A range of risk and protective factors for DSH were examined using multivariate analyses.The prevalence of DSH in the past year was 1.53% in Grade 7 and .91% in Grade 9 for males and 4.12% and 1.34% for Grade 7 and Grade 9 females, respectively, with similar rates across states. In multivariate analyses, incident DSH was lower in Washington State (odds ratio [OR] = .67; 95% confidence interval [CI] = .45-1.00) relative to Victoria 12 months later. Risk factors for incident DSH included being female (OR = 1.93; CI = 1.35-2.76), high depressive symptoms (OR = 3.52; CI = 2.37-5.21), antisocial behavior (OR = 2.42; CI = 1.46-4.00), and lifetime (OR = 1.85; CI = 1.11-3.08) and past month (OR = 2.70; CI = 1.57-4.64) alcohol use relative to never using alcohol.Much self-harm in adolescents resolves over the course of 12 months. Young people who self-harm have high rates of other health risk behaviors associated with family and peer risks that may all be targets for preventive intervention.