INS and Hypoglycemia: Insulin autoimmune syndrome (IAS, Hirata disease) is a rare cause of hyperinsulinaemic hypoglycaemia characterised by insulin-binding autoantibodies in exogenous insulin-naïve individuals.1,2 In affected patients, antibody binding reduces the action of acutely secreted insulin and delays clearance of plasma insulin resulting in increased insulin concentration with raised insulin/C-peptide molar ratio.1,3,4 Insulin immunocomplexes act as reservoirs, with insulin–glucose mismatch leading to post-prandial and/or fasting hypoglycaemia.