Background The emergency department (ED) is a crucial encounter point in cancer care. Yet, data on the causes of ED visits are limited in patients treated with immune checkpoint inhibitors (ICI). Therefore, we evaluated ED visits in patients treated with ICIs in attempt to determine the predisposing factors. Methods We performed a retrospective chart review on adult cancer patients treated with ICIs for any type of cancer in the Hacettepe University Cancer Center. The data on ED visits after the first dose of ICIs to 6 months after the last cycle of ICIs were collected. Results A total of 221 patients were included in the study. The mean age was 58.46 +/- 13.87 years, and 65.6% of patients were males. Melanoma was the most common diagnosis (27.6%), followed by kidney and lung cancers. Eighty-three of these patients (37.6%) had at least one emergency department (ED) visit. Most of the ED visits were related to symptoms attributable to the disease burden itself, while immune-related adverse events comprised less than 10% of these visits. While baseline Eastern Cooperative Oncology Group performance status, age, polypharmacy, concomitant chemotherapy, eosinophilia, and lactate dehydrogenase levels did not significantly increase the risk, patients with regular opioid use and baseline neutrophilia (> 80,000/mm(3)) had a statistically significant increased risk of visiting the ED (p = 0.001 and 0.19, respectively). These two factors remained significant in the multivariate analyses. Conclusion In this study, almost 40% of ICI-treated patients had ED visits. Collaboration with other specialties like emergency medicine is vital for improving the care of patients receiving immunotherapy.