Suicidal thoughts and behaviors often onset during adolescence, constituting a major public health concern. Despite rising rates in youth, psychotherapeutic and pharmacological treatment outcomes remain meager, indicating a need to identify modifiable risk factors. Experts suggest sleep may serve as a promising clinical indicator of risk and treatment progress, yet few studies have examined acute temporal associations between sleep and suicidal ideation. Participants were depressed and suicidal adolescents (age 13-19, n = 311) attending an intensive outpatient program (IOP). Patients completed weekly self-report assessments of sleep, depression, and suicidal ideation throughout IOP, with an average of 5 assessments over 30 days. Greater overall sleep difficulties, as well as within-person increases in sleep difficulties, were predictive of greater depression severity and suicidal ideation at subsequent assessments, above and beyond previous levels of symptoms. The reverse associations were not found. Inclusion of within-person changes in sleep difficulties significantly improved model fit compared to inclusion of overall sleep difficulties alone. This study provides additional evidence for a prospective relationship between worsening sleep difficulties and suicidal ideation in an IOP youth sample. Worsening sleep may be an important clinical indicator of subsequent depression and suicide risk among adolescents in treatment.