ObjectiveTo describe a case of testicular neoplasia and alopecia universalis in a dog, and successful treatment of the latter with ciclosporin.AnimalTwelve‐year‐old intact male wirehaired fox terrier.MethodsCastration, skin biopsy for histopathology, lymphocyte immunophenotyping and clonality analysis of the canine T‐cell receptor gamma locus (TCRγ) rearrangement.ResultsThe dog presented with symmetrical generalized alopecia. Testicular enlargement was noted which on castration was determined to be caused by bilateral interstitial cell tumours, Sertoli cell tumours and a unilateral seminoma. During the four months after castration the alopecia became more severe and widespread. Histopathology of the skin showed moderate, multifocal, mural folliculitis, peribulbar mucinosis and lymphocytic bulbitis, and targeting of anagen hair follicles. Immunophenotyping of the infiltrate showed a population of well‐differentiated, small CD3‐positive T lymphocytes, some expressing CD4 and others CD8. Molecular analysis revealed a polyclonal lymphocytic infiltrate, substantiating the diagnosis of alopecia areata rather than lymphoma. Treatment with ciclosporin (4.6 mg/kg) and ketoconazole (4.6 mg/kg) resulted in complete hair regrowth.Conclusion and clinical importanceCiclosporin treatment, in combination with ketoconazole, can be effective for treatment of alopecia universalis in the dog. Alopecia universalis may present with clinically noninflammatory, symmetrical, generalized alopecia, mimicking an endocrine alopecia, and skin biopsies are needed to confirm the diagnosis.