Hyperglycemic hyperosmolar syndrome (HHS) is a clinical entity not identical to diabetic ketoacidosis (DKA), and with a markedly higher mortality. Children with HHS can also present with concomitant DKA. Patients with HHS (with or without DKA) are profoundly dehydrated but often receive inadequate fluid resuscitation as well as intravenous insulin therapy based on traditional DKA protocols, and this can lead to devastating consequences. In this article, we briefly review HHS along with a report of an adolescent who presented with HHS and DKA and was initially managed as DKA. She went into hypotensive shock and developed severe, multiorgan failure. A thorough understanding of the pathophysiology of HHS and its differences from DKA in terms of initial management is crucial to guide management and improve outcomes. Additionally, fluid therapy in amounts concordant with the degree of dehydration remains the mainstay therapy.