Abstract The human Insulin Receptor (INSR) mutation can result in inherited insulin resistance syndrome. Severe Insulin Resistance (IR) results secondary INSR mutations have been reported in adult, adolescent and children manifesting with Hyperinsulinemic Hypoglycaemia (HH). Rabson-Mendenhall Syndrome and Donohue’s Syndrome, Type A insulin resistance syndrome are resultant of the INSR mutation. We report a case of an adolescent boy who presented with very high blood sugars requiring high doses of insulin, with a novel heterozygous INSR mutation.