The hypothalamus is involved in a variety of autonomic, endocrine, neurological and behavioural functions including temperature, osmostatic and autonomic nervous system regulation, pituitary, thyroid, adrenal and gonadal control, thirst, appetite and weight control, memory and emotional behaviour including aggression and laughter, and biological (circadian) rhythms. The functional anatomy of the hypothalamus and its major afferent and efferent neurological connections are described, with particular reference to hypothalamic hamartomas (HH), gelastic seizures, MRI of the hypothalamus, and potential effects of surgery for HH. Normal development of the hypothalamus is reviewed in relation to models of forebrain development, descriptive hypothalamic embryology and the importance of known transcription factors. Potential environmental antecedents to HH development are discussed, and the significance for sporadic, isolated HH of several syndromes associated with HH is explored.