This study sought to examine the prevalence of insomnia and its association with depression, anxiety, and medical comorbidities in patients after an acute coronary syndrome (ACS). Insomnia increases risk of recurrent cardiac events in ACS patients, but little is known about the prevalence and clinical correlates of insomnia in this setting. Patients (n = 102, 58.3 ± 10.6 years-old) admitted for ACS to a cardiology service at an urban academic medical center completed the Insomnia Severity Index, Epworth Sleepiness Scale, and measures of depression and anxiety. A subset (n = 20) completed ambulatory polysomnography (PSG) in their homes several weeks after discharge. Moderate or severe insomnia was reported by 37% of patients during hospitalization and was associated with 76 minutes more wake after sleep onset measured by home PSG. Although depression and insomnia were strongly associated, about 1 in 4 patients with insomnia did not report significant depressive symptoms. Sleep apnea was documented in 80% of patients on PSG, but insomnia was not associated with sleep apnea, periodic limb movements, demographic factors, or medical conditions other than liver disease. Insomnia is present in over one-third of ACS patients during hospitalization, but at-risk patients could not be readily identified by demographic or medical factors or by depression symptoms.