Erysipelothrix rhusiopathiae causes sporadic, often fatal septicaemia in cetaceans; published cases rest almost entirely on cultured isolates, and none has included post-mortem imaging. We investigated a juvenile male short-beaked common dolphin (Delphinus delphis) stranded on Jeju Island, Republic of Korea, using post-mortem computed tomography (PMCT) of the frozen carcass, necropsy, histopathology and tiered molecular testing. Rhomboid skin lesions extended through the skin into the blubber. PMCT documented gravity-dependent pulmonary opacification, fluid in the trachea and bronchi, peritoneal effusion, no decomposition gas and a gastric fishing hook, confirmed at necropsy. Culture was not attempted because the carcass had been stored frozen. Erysipelothrix spp. DNA was detected by broad-range 16S rRNA sequencing in 11 of 12 tissues, and E. rhusiopathiae was identified by species-specific PCR and amplicon sequencing in all 12 tissues, yielding one identical 356-bp sequence. Histopathology showed epidermal coagulative necrosis with septal panniculitis and abundant Gram-positive bacteria throughout the lesion, pulmonary haemorrhage and oedema, interstitial nephritis and reactive lymphadenitis, consistent with fatal septicaemia. The case provides imaging correlates of erysipelas, a culture-independent diagnostic framework for frozen carcasses and a tissue-by-tissue molecular dataset; the relationship of the strain to other Korean cetacean isolates remains to be established genomically.