AbstractObjectiveTo describe a case of Waterhouse–Friderichsen syndrome of adrenocortical failure in a cat with Klebsiella spp. infection.Case SummaryA 12‐year‐old male neutered domestic short‐haired cat was referred for respiratory failure requiring mechanical ventilation. The cat remained comatose despite successful weaning from the ventilator and developed a Klebsiella pneumoniae pneumonia. On day 4 of hospitalization, the cat acutely deteriorated with profound hypotension, azotemia, and hyperkalemia, which rapidly progressed to cardiac arrest. Necropsy findings revealed massive adrenal hemorrhage and intralesional bacteria, termed Waterhouse–Friderichsen syndrome. Waterhouse–Friderichsen syndrome was suspected to have been the cause of acquired adrenocortical insufficiency and sudden death of the cat.New or Unique InformationTo the authors’ knowledge, this is the first report of sepsis causing Waterhouse–Friderichsen syndrome in a veterinary species.