Background: Given reports of the adverse effects of COVID-19 on adolescent mental health, it is critical to understand how it impacts psychiatrically hospitalized youth who may be particularly vulnerable to its effects. Objective: This study aimed to advance our understanding of high-risk adolescents' experiences of COVID-19, including COVID-19-related stress, changes in daily functioning, and coping as they relate to suicidal ideation (SI). Method: Participants were 107 youth (ages 11-18; M = 15.06, SD = 1.79) admitted to an adolescent psychiatric inpatient unit during the time when the initial COVID-19 safety measures (i.e., school closure, stay-at-home-order) and reopening initiatives (Phase I, II, and III) were implemented in Rhode Island between March 13th and July 19th 2020. Adolescents completed measures of COVID-19-related stress, coping, functioning, and SI at the time of admission. Results: Nearly half of the sample (43%) reported a negative impact of COVID-19 on daily functioning. Youth who endorsed COVID-19-related decline in functioning evidenced higher levels of SI compared to youth with no change or improvement in functioning due to COVID-19. Overall levels of stress were not associated with SI. Greater coping repertoire, but not the use of specific coping strategies was associated with higher levels of SI. Conclusions: Findings demonstrate the importance of examining COVID-19-related changes in functioning and broadening repertoire of coping strategies among adolescents at high risk for SI.