Introduction. Insomnia is an important symptom associated with major depressive disorder (MDD). In addition, it is one of the risk factors for suicide. Studies have shown the relationship be-tween insomnia and suicidal behavior in patients with MDD. However, this association has not been evaluated in a large sample of hospitalized patients. Objectives. To evaluate the suicidal be-havior in MDD patients with insomnia compared to those without insomnia. Methods. From the National Inpatient Sample (NIS 2006–2015) database using the ICD-9 code, patients’ data were obtained with the primary diagnosis of MDD and comorbid diagnosis of insomnia disorders (MDD+I). These patients were compared with MDD patients without insomnia disorders (MDD–I) by performing a 1:2 match for the primary diagnosis code. Suicidal ideation/attempt da-ta were compared between the groups by multivariate logistic regression analysis. Results. After the diagnostic code matching, 139061 patients were included in the MDD+I group and 276496 patients in the MDD–I group. MDD+I patients were older (47 years vs. 45 years, p < 0.001) com-pared to the MDD–I group. The rate of suicidal ideation/attempt was 56.0% in the MDD+I group and 42.0% in the MDD–I group (p < 0.001). After adjusting for age, sex, race, borderline personal-ity disorders, anxiety disorders, and substance use disorders, ‘insomnia’ was associated with 1.71 times higher odds of suicidal behavior among MDD patients admitted to the hospital. (Odds ratio: 1.71, 95% confidence interval 1.60–1.82, p < 0.001). Conclusions. Insomnia among MDD patients is significantly associated with the risk of suicide. MDD patients with insomnia need to be closely monitored for suicidal behavior.