PURPOSE Emergency department observation units (EDOUs) have been shown to decrease length of stay and improve cost effectiveness. Yet, compared with noncancer patients, patients with cancer are placed in EDOUs less often. In this study, we aimed to describe patients who were placed in a cancer center's EDOU to discern their clinical characteristics and outcomes. METHODS We performed a retrospective observational study that included all patients age 18 years and older who presented to our emergency department (ED) and were placed in the EDOU between March 1, 2019, and February 29, 2020. The patients' electronic medical records were queried for demographics, comorbidities, diagnosis at the time of placement in the EDOU, length of stay, disposition from the EDOU, ED return within 72 hours after discharge from the EDOU, and mortality outcomes at 14 and 30 days. RESULTS A total of 2,461 visits were eligible for analysis. Cancer-related pain was the main reason for observation in more than one quarter of the visits. The median length of stay in the EDOU was approximately 23 hours, and 69.6% of the patients were discharged. The ED return rate for unscheduled visits at 72 hours was 1.9%. The 14- and 30-day mortality rates were significantly higher for patients who were admitted than for those who were discharged (14 days: 1.7% v 0.3%, P < .001; 30 days: 5.9% v 1.8%, P < .001). CONCLUSION Our data suggest that placing patients with cancer in EDOUs is safe, reduces admissions, and reserves hospital resources for patients who can receive the most benefit without compromising care.