Abstract: Background: Rates of suicide in United States Marines are among the highest in the military, and sleep disorder symptoms are a known risk factor for suicide in the military. Intensive ecological momentary assessments (EMA) might improve the ability to detect periods that are characterized by increased suicidal ideation. Marines who were at high risk for suicide were intensively assessed for one month on sleep, suicidal urges, posttraumatic stress disorder (PTSD) and depression symptoms. Methods: U.S. Marines (N = 40) who had a past month suicide attempt or suicidal urges with intent were sent EMA for 28 days. Mixed effects models explored associations among daily sleep, suicidal urges, PTSD, and depression symptoms. Results: Worsened sleep indicators on a given night significantly predicted higher maximum values of suicide urges the following day. Worse sleep quality the prior night was moderately associated with more severe PTSD symptoms and depression symptoms. Greater severity of PTSD symptoms and depression symptoms were strongly associated with both the maximum value and the range of suicide urges. PTSD and depression symptoms mediated the relationship between sleep quality and suicidal urges. Participants reported that 0000-0300 had the greatest elevation in endorsement of highest suicide urges. Limitations: This study had a small sample size may not generalize beyond active duty Marines. Conclusions: Poor sleep quality and other sleep markers were an important risk factor for suicidal urges among U.S. Marines. This relationship was mediated by exacerbations in PTSD and depression symptoms. Interventions are needed to interrupt suicide risk during and following nights with poor sleep.