The authors developed the Self-Injurious Thoughts and Behaviors Interview (SITBI) and evaluated its psychometric properties. The SITBI is a structured interview that assesses the presence, frequency, and characteristics of a wide range of self-injurious thoughts and behaviors, including suicidal ideation, suicide plans, suicide gestures, suicide attempts, and nonsuicidal self-injury (NSSI). This initial study, based on the administration of the SITBI to 94 adolescents and young adults, suggested that the SITBI has strong interrater reliability (average kappa = .99, r = 1.0) and test-retest reliability (average kappa = .70, intraclass correlation coefficient = .44) over a 6-month period. Moreover, concurrent validity was demonstrated via strong correspondence between the SITBI and other measures of suicidal ideation (average kappa = .54), suicide attempt (kappa = .65), and NSSI (average kappa = .87). The authors concluded that the SITBI uniformly and comprehensively assesses a wide range of self-injury-related constructs and provides a new instrument that can be administered with relative ease in both research and clinical settings.