A 4-year-old female guinea pig was presented with pruritic, erythematous, hypotrichotic and scaling skin lesions, mainly involving the abdomen and the hindlegs. Clinical abnormalities were limited to the skin, and the guinea pig was otherwise healthy. The dermatological diagnostic work-up excluded ectoparasites, dermatophytosis and an endocrinopathy as differential diagnoses for the pruritus and hair loss. An allergic dermatitis was under investigation when the general and skin condition deteriorated. A neoplastic skin disorder was suspected, and skin biopsies revealed changes consistent with a cutaneous epitheliotropic T-cell lymphoma. Pautrier's microabscesses and immunophenotyped CD3(+) CD79(-) lymphocytes were identified. Owing to the deteriorating condition of the animal and the unknown but most likely poor prognosis of this disease, the guinea pig was euthanized. To the authors' knowledge, this is the first case report of cutaneous epitheliotropic T-cell lymphoma in the guinea pig with characteristic histopathological and immunohistochemical features.