Multiple endocrine neoplasia (MEN) embodies a group of diseases in human patients and domestic animals that are characterized by neoplasia of two or more endocrine tissues. In humans, MEN is grouped into three major syndromes: MEN-1, MEN2A, and MEN-2B. MEN-1 is an autosomal dominant hereditary syndrome resulting from the mutation of the menin gne, which codes for a protein involved in transcription inhibition. The various mutations identified in the menin gene sequence of patients with MEN-1 have indicated correlation with development of different tumor phenotypes. MEN-like syndromes in dogs, cats, horses, bulls, and ferrets have been reported. The presented case report described a simultaneous occurrence of malignant insulinoma and thyroid adenocarcinoma in a seven-year-old, female Irish Setter with the episodes of weakness and collapses.