The Somogyi phenomenon or effect is a paradoxical situation of insulin-induced post-hypoglycemic hyperglycemia. The historical aspects of this phenomenon and the subsequent hypotheses and controversy are reviewed. The clinical situation is explained, with regard to its recognition, management and importance as an etiological factor in ‘brittle’ diabetes. Hormone immunoassay techniques at present show human growth hormone (HGH) to be the major consequence of insulin-induced hypoglycemia leading to post-hypoglycemia glucose intolerance, but further studies will probably show glucagon to have a major role.