In a 10-year-old ovariohysterectomized standard Schnauzer, the finding of dexamethasone-resistant hypersecretion of cortisol, the results of computed tomography, and elevated plasma concentrations of ACTH suggested the presence of both adrenocortical tumour and pituitary-dependent hyperadrenocorticism. The dog made an uneventful recovery after bilateral adrenalectomy and remained in good health for 31/2 years with substitution for the induced hypoadrenocorticism. Then the enlarged pituitary caused neurological signs and eventually euthanasia was performed. The surgically excised right adrenal contained a well-circumscribed tumour of differentiated adrenocortical tissue and in the left adrenal there were two adrenocortical tumours and a pheochromocytoma. The unaffected parts of the adrenal cortices were well developed and without regressive transformation. At necropsy there were no metastatic lesions. The cells of the pituitary tumour were immunopositive for ACTH and had characteristics of malignancy. The present combination of corticotrophic tumour, adrenocortical tumours, and pheochromocytoma may be called 'multiple endocrine neoplasia' (MEN), but does not correspond to the inherited combinations of diseases known in humans as the MEN-1 and the MEN-2 syndromes. It is suggested that the co-existence of hyperadrenocorticism and pheochromocytoma may be related to the vascular supply of the adrenals. Some chromaffin cells of the adrenal medulla are directly exposed to cortical venous blood, and intra-adrenal cortisol is known to stimulate catecholamine synthesis and may promote adrenal medullary hyperplasia or neoplasia.