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 κ=. 99, r= 1.0) and test–retest reliability (average κ=. 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 κ=. 54), suicide attempt (κ=. 65), and NSSI (average κ=. 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.