Diabetes Mellitus affects the pancreas and Diabetes Insipidus affects the kidneys. Diabetes Mellitus is a condition that causes the pancreas to produce little or no insulin.lso called non-insulin-dependent diabetes, type 2 diabetes. Diabetes insipidus (DI) is unrelated to diabetes mellitus and has nothing to do with glucose. The symptoms include excessive thirst and constant urination because of the inability of the kidneys to regulate fluid.