Background and Objectives: The COVID-19 pandemic was associated with major disruptions, not only at the environmental, social, and economic levels but also in the public health systems and, therefore, emergency care utilisation. Prior to the pandemic, one of the most significant issues in the ED was overcrowding, with a consequent percentage of people leaving the ED without being seen (LWBS). The aim of this study was to assess the association between the 2020 COVID-19 pandemic and the number of LWBS, compared with the rates recorded during the same period in 2019 and 2021. Materials and Methods: A retrospective comparative observational study of ED admissions was conducted in two university hospitals in Ancona (Italy) between 9 March and 3 May 2020 and in Gran Canaria (Spain) between 14 March and 10 May 2020, corresponding to the lockdown in the two countries, respectively. ED visits were assessed during the defined periods, separately for the Italian and Spanish contexts and between groups, comparing the two contexts for each year. Results: In Italy, during the 2019 timeframe, 597 (7.0%) of 8568 patients who arrived in the ED left before being seen; during the same period in 2020, 100 (3.2%) of 3100; and in 2021, 334 (6.0%) of 5555. In Spain, patients leaving the ED prior to medical consult in 2019 were 567 (4.0%) out of 14,034 visits; in 2020, they amounted to 185 (2.6%) out of 7208; and in 2021, they were 528 (4.0%) out of 13,214. The results of the logistic regression analysis for Italy and Spain showed that male sex [odds ratio (OR), 95% confidence interval (CI): 1.38 (1.24–1.53)], age group between 17 and 43 years compared to those subjects older than 74 years old [OR (95%CI): 4.04 (3.34–4.88)] and a lower priority code at triage were significantly associated with a higher odds of LWBS. Conclusions: The findings suggest that the COVID-19 pandemic was associated with changes in only some characteristics of the profiles and types of patients leaving the ED, while it had a strong impact on the number of patients who left the ED before medical examination. The observed decrease in ED visits and LWBS rates in 2020 suggests that the COVID-19 pandemic has changed the population’s use of the ED, highlighting the potential need for improved public and professional awareness of appropriate care pathways and the role of health professionals in them.