A hormone is a chemical messenger, released from one part of the body, travelling to an often-distant location to deliver instructions elsewhere in a very targeted manner. The endocrine system comprises multiple glands including the anterior and posterior pituitary (which together comprise the ‘master gland’), the thyroid, the parathyroids, the adrenals, the kidney, the heart, the pancreas, and the gonads. These glands can be hit by anything in the surgical sieve from haemorrhage, infection, and malignancy, through to an autoimmune attack. Disease often manifests in terms of patterns of hypo- or hyper-function of particular hormones and subsequently treatment of endocrine disease is often based around managing the replacement of a deficient hormone e.g. insulin in diabetes, or suppression of an overactive hormone e.g. using anti-thyroid medication in the context of thyrotoxicosis. The expert Endocrinologist is able to identify the gestalt of such patterns and interpret the appropriate dynamic tests to elucidate the underlying problem. In this chapter we’ll focus on what to ask when faced with symptoms of endocrine gland dysfunction. Many of these diseases are subtle and insidious so special attention needs to be paid by the discerning medical historian.