The COVID-19 pandemic led to unprecedented numbers of patients seen in the emergency department (ED), some who had COVID-19, some who had a different diagnosis, and some who had both. This study analyzes patients who presented to the ED with COVID-19 and signs of another diagnosis that was missed. Approximately one-third of patients with a second concurrent diagnosis experienced a diagnostic delay. Factors that may have influenced the missed diagnosis include ED overcrowding and anchoring heuristics.