Impaired insulin secretion and insulin resistance are the two main mechanisms leading to type 2 diabetes mellitus. Insulin exerts multiple effects upon target cells, especially skeletal muscle, liver, and adipose tissue. In general, insulin promotes storage of glucose and inhibits the breakdown of stored glycogen into glucose. The counter regulatory hormones glucagon, catecholamine, cortisol and growth hormone are released during hypoglycemia and under other stress conditions. These hormones have insulin-antagonistic effects both in the liver and in the peripheral tissues. A significant number of endocrine disorders is associated with varying degrees of glucose intolerance, with which sustained excess of these hormones is associated. Indeed, type 2 diabetes is frequently observed in patients with various hormonal diseases including acromegaly, Cushing syndrome, pheochromocytoma, hyperthyroidism, and glucagonoma. In particular, improvement of glycemic control following treatment for these hormonal diseases confirms a causal relationship between excess of these hormones and diabetes. In this review, there will be a discussion over these endocrine diseases in relation to diabetes.