Objective: To identify the impact of a mass gathering event (MGE) on emergency department (ED) patient presentations with communicable diseases and underpinning syndromic indicators (SIs). Methods: This retrospective observational cohort study was undertaken in one large public teaching hospital ED in Queensland, Australia. Routinely collected ED data for patient presentations with an ICD-10 diagnosis corresponding to a communicable disease were used to compare demographic characteristics, clinical characteristics, and outcomes before (March 23 to April 3), during (April 4 to April 15), and after (April 16 to April 27) the 2018 Commonwealth Games. Results: Over the study period, there were 10 595 patient presentations to the ED; 14.2% (n = 1503) were diagnosed with a communicable disease. The median age of those with a communicable disease was 8 years, 50.5% (n = 759) were female, and 24.8% (n = 373) arrived by ambulance. The most common communicable disease profile was respiratory in nature (51.4%, n = 772). The most common SI was altered breathing (24.0%, n = 185). ED length of stay (LOS) increased over the study period (pre: 160 min; during: 163 min; post: 180 min, p < 0.001). Conclusions: The 2018 Commonwealth Games had an impact on ED presentations with communicable diseases, in terms of LOS. A longer LOS and higher percentage of patients with a LOS of more than 4 hrs in the ED were noted following the MGE period. This outcome indicates a potential need to continue with up-scaled services. Future research is required to understand the broader impact on other EDs in the area, and longitudinal patient follow-up is needed to determine the potential spread of communicable diseases.