This study examines the association of self-reported impulsivity to nonsuicidal self-injury, suicidal ideation, suicide attempts, and completed suicides in a clinical sample of 508 Finnish adolescents (aged 12–17) treated in psychiatric inpatient care between April 2001 and March 2006. The Schedule for Affective Disorder and Schizophrenia for School-Age Children Present and Lifetime interview was used to gather information on psychiatric disorders, impulsivity, and suicidality of the adolescents. Mortality data were obtained from the national cause of death register. In adolescent girls, impulsivity was significantly associated with suicidal ideation and attempts and completed suicides in adolescent boys. Of adolescent boys with impulsivity, 10.4% had died by suicide during the follow-up time. For preventive purposes, health care professionals are encouraged asked adolescents targeted questions about impulsivity and to consider the associated risk of suicidality identified in this study.