Objectives: This study aimed to determine the incidence and post-discharge resolution of new-onset insomnia in hospitalised patients with no previous history of insomnia, as well as to define major correlates of in-hospital insomnia. Methods: This prospective observational study was conducted between November 2019 and January 2020 at a tertiary care centre in Lebanon. All hospitalised patients >18 years of age with no history of insomnia were screened for new-onset insomnia using the Insomnia Severity Index (ISI) scale. Subsequently, patients were re-assessed two weeks after discharge to determine insomnia resolution. Results: A total of 75 patients were included in the study. Of these, nine (12%) had no insomnia, 34 (45.3%) had subthreshold insomnia, 22 (29.3%) had moderate insomnia and 10 (13.3%) had severe insomnia. The mean ISI score was 14.95 ± 6.05, with 88% of patients having ISI scores of >7 (95% confidence interval: 0.822–0.965). The frequency of new-onset insomnia was significantly higher among patients who shared a room compared to those in single-bed rooms (95.7% versus 75%; P = 0.011). Other factors were not found to be associated with new-onset insomnia, including the administration of medications known to cause insomnia, in-hospital sedative use, overnight oxygen, cardiac monitoring and self-reported nocturnal toilet use. Overall, insomnia resolution occurred in 78.7% of patients two weeks after discharge. Conclusion: There was a high incidence of acute new-onset insomnia among hospitalised patients at a tertiary centre in Lebanon. Additional research is recommended to further examine inhospital sleep disturbance factors and to seek convenient solutions to limit insomnia. Keywords: Sleep Wake Disorders; Insomnia; Hospitalization; Incidence; Risk Factors; Lebanon.