After describing short functional anatomy, common and important diseases of pituitary, thyroid, pancreas and adrenal are described. These include causes of hypo and hyper pituitarism, clinical manifestations of functional pituitary adenoma and its complications. Common diseases of thyroid including congenital anomalies, thyroiditis, simple and multinodular goiter, different types of thyroid carcinoma with their etiopathogenesis, genetic association, gross and microscopic features, diagnostic modalities and importance of an solitary nodule are written here. Etiopathogeneis of acute and chronic pancreatitis, pancreatic cyst formation, pancreatic enzyme levels, gross and microscopic features of pancreatic carcinoma and diagnostic modalities are also incorporated. Most important diseases of endocrine pancreas- Diabetes mellitus, its classification, etiopathology, complications and diagnostic modalities are described. Hyper and hypo adrenalism, their clinical manifestations, etiological factors and important adrenal syndromes like Cushing and Conn syndrome, adrenogenital syndrome and pheochromocytoma with their clinical features and diagnostic modalities have been described in this chapter.