Background: Insomnia is common in hospitalized patients. However, no study has examined new onset of insomnia in patients without a prior history of insomnia. Objectives: Incidence of new onset of insomnia in inpatients, associated factors and resolution rate after 2 weeks. Method: This is a prospective observational study conducted at a community hospital. We used the Insomnia Severity Index questionnaire to screen for insomnia in all patients located in the general medical floors from day 3 to day 5 of their hospital stay. We excluded patients with a prior insomnia history. Results: Out of the 205 patients who met the inclusion criteria, 75 patients (36%) reported insomnia. Severe insomnia was present in 3% of patients. Difficulty in maintaining sleep is the most common symptom. Frequent staff disruptions due to blood draws and vital signs checks were reported by 68% as the cause of insomnia, followed by illness associated causes (64%) and sleep disruption due to noise and or brightness (23%). Patients with insomnia had more awakenings due to noise, brightness, and staff interruptions than those without insomnia (1.35 times vs. 0.9 times, p = 0.027). Patients with respiratory symptoms, cardiac monitoring, oxygen use, private rooms, and no sedative use did not have a higher insomnia risk. Patients with insomnia had significant lower satisfaction scores than patients without insomnia (4.53 vs. 4.05, p = 0.001) but did not have a different length of stay (6.18 vs. 6.19, p = 0.97). In 31% of patients with insomnia who were able to be contacted two weeks after discharge, 75% of them had insomnia resolution. Conclusion: New onset of insomnia occurred in 36% of hospitalized patients. Most common causes are staff disruption and disease symptoms. It was usually short-term and could decrease patients' satisfaction score.