Background: 'Capnocytophaga canimorsus', a Gram-negative rod, belongs to the Flavobacteriaceae family and colonizes the oropharynx of dogs and cats. Infections with 'C. canimorsus' are rare and can induce a systemic infection with a severe course of the disease. So far, only five case reports of 'C. canimorsus' infections associated with Waterhouse–Friderichsen Syndrome (WFS) have been reported with only two of the patients having a history of splenectomy. Case presentation: Here, we report a fatal case of WFS due to 'C. canimorsus' bacteremia and mycetal superinfection in a 61-year-old female asplenic patient. Despite extensive therapy including mechanical ventilation, antibiotic coverage with meropenem, systemic corticosteroids medication, vasopressor therapy, continuous renal replacement therapy, therapeutic plasma exchange, multiple transfusions of blood products and implantation of a veno-arterial extracorporeal membrane oxygenation the patient died 10 days after a dog bite. The autopsy showed bilateral hemorrhagic necrosis of the adrenal cortex and septic embolism to heart, kidneys, and liver. Diagnosis of 'C. canimorsus' was prolonged due to the fastidious growth of the bacteria. Conclusions: The occurrence of a severe sepsis after dog bite should always urge the attending physician to consider 'C. canimorsus' as the disease-causing pathogen. A therapeutic regimen covering 'C. canimorsus' such as aminopenicillins or carbapenems should be chosen. However, despite maximum therapy, the prognosis of 'C. canimorsus-induced' septic shock remains very poor. Asplenic or otherwise immunocompromised patients are at higher risk for a severe course of disease and should avoid exposure to dogs and cats and consider antibiotic prophylaxis after animal bite.