A 53-year-old female with severe headache, obesity, and type 2 diabetes mellitus is diagnosed with a pituitary tumor that is considered to be non-functioning; however, following pituitary surgery, the tumor stains weakly for adrenocorticotrophin (ACTH), is TPIT positive, and has a Ki-67 of 4%. This evidence concerns the gene MKI67 and diabetes mellitus.