As sleep problems have been identified as an important, yet understudied, predictor of suicide risk, the present study analyzed the relationship between daytime sleepiness and nighttime sleep disturbance in a high-risk population of adults admitted to an inpatient psychiatric hospital. Objectives were to (1) examine the time course of subjective daytime sleepiness, nighttime sleep disturbance, and suicide risk throughout inpatient psychiatric treatment, (2) examine pre- to post-treatment changes in sleep disturbance with treatment as usual in an inpatient psychiatric setting, and (3) investigate whether daytime sleepiness and nighttime sleep disturbance predicted suicide risk above and beyond anxiety and depression. Participants were 500 consecutively admitted adults admitted to an intermediate length of stay (4–6 weeks) inpatient psychiatric hospital (47% female; 18–87 years of age). Measures of sleep, suicide risk, depression, and anxiety were completed at admission, weeks 1 through 4, and at discharge. Latent growth curve modeling (LGM) and hierarchal linear modeling (HLM) were conducted. The LGM analysis demonstrated that daytime sleepiness, nighttime sleep disturbance, and suicide risk all improved throughout inpatient treatment. Further, HLM showed that daytime sleepiness predicted suicide risk above and beyond symptoms of anxiety, depression, major sleep medications, and prior suicidal ideation and attempts, while nighttime sleep disturbance predicted suicide risk above and beyond symptoms of anxiety, major sleep medications, and prior suicidal ideation and attempts. Findings indicate the need to reevaluate safety protocols that may impact sleep, particularly that may increase daytime sleepiness, and to develop evidence-based sleep interventions for individuals admitted to inpatient psychiatric hospitals.