Hypopituitarism is defined as one or more pituitary hormone deficits due to a lesion in the hypothalamic-pituitary region. By far, the most common cause of hypopituitarism associated with a sellar mass is a pituitary adenoma. A high index of suspicion is required for diagnosing hypopituitarism in several other conditions such as other massess in the sellar and parasellar region, brain damage caused by radiation and by traumatic brain injury, vascular lesions, infiltrative/immunological/inflammatory diseases (lymphocytic hypophysitis, sarcoidosis and hemochromatosis), infectious diseases and genetic disorders. Hypopituitarism may be permanent and progressive with sequential pattern of hormone deficiencies (radiation-induced hypopituitarism) or transient after traumatic brain injury with possible recovery occurring years from the initial event. In recent years, there is increased reporting of less common and less reported causes of hypopituitarism with its delayed diagnosis. The aim of this review is to summarize the published data and to allow earlier identification of populations at risk of hypopituitarism as optimal hormonal replacement may significantly improve their quality of life and life expectancy.