Although most children with coronavirus disease 2019 (COVID-19) are asymptomatic or only with mild symptoms, many symptomatic children still require admission to the intensive care unit. Multiple cases of diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic syndrome (HHS) associated with COVID-19 have been reported in adults. However, to our knowledge, only few similar cases have been published in the pediatric population. We report one of the first few severe cases of mixed HHS with DKA associated with COVID-19 in an adolescent. Our patient was successfully treated with intravenous immunoglobulin, Remdesivir, and methylprednisolone. As the pandemic continues, clinicians should be aware of this syndrome and consider early use of Remdesivir and corticosteroids. Further studies are required to understand the pathophysiology of this syndrome occurring with COVID-19.