Aim of the study: The aim of the study is to investigate the arrival frequency of patients who visit Osijek Clinical Hospital Centre Emergency Department, but do not require urgency treatment, since they are classified as 4th and 5th triage categories according to the ATS triage scale. Study design: A cross-sectional study with historical data. Materials and methods: A retrospective data analysis was performed for patients who were medically treated and triaged through the Emergency Department (ED) of the Osijek Clinical Hospital Centre in 2023. The analysis of triage forms and hospital medical documentation recorded in the hospital information system provided data on the frequency of assigned triage categories, efficiency indicators, waiting time until the start of the medical examination, examination time, type of arrival and discharge status of patients in the Emergency Department. Results: A total of 77.5% of patients who visited the ED in 2023 were classified into the fourth and fifth triage categories, and the fourth category was the most commonly represented with 71.7% of patients. The efficiency indicators were within the defined thresholds according to the ATS triage scale. All patients in the first triage category were examined immediately. The median waiting time for a medical examination was within the maximum permissible values for all categories, with triage categories 4 and 5 having the longest median waiting time of 20 minutes. The examination time was longest in triage category 2 with a median value of 200 minutes. Patients most frequently came to the emergency department independently and without a referral, especially patients in triage categories 4 and 5. After they were examined and the necessity for urgent care excluded, 72.2% of patients were discharged. Conclusion: Based on the collected data, it can be concluded that the emergency department is overcrowded with patients classified as the fourth and fifth triage categories, whose health condition does not require urgent treatment and care and who come to the emergency department independently and without referral. This threatens patient safety and quality of care in the Emergency Department, so organizational changes to the hospital emergency service system are necessary.