A 5-year-old male Shiba dog with progressive neurologic signs was examined by computed tomography (CT). A CT image of the brain disclosed a large, spherical high-density lesion in the thalamus and diencephalon. Serum LH, FSH and testosterone levels were all low. Macroscopically the large mass was connected with the sella turcia, and it was histopathologically diagnosed as a pituitary chromophobe carcinoma. An aspermatogenesis was observed in the testes. Therefore, it was suggested that the low levels of gonadotropin secretion from the pituitary gland due to the pituitary tumor resulted in the failure of maturation of spermatozoa and spermatids.