Diabetes mellitus is a metabolic disease characterised by chronically high glucose levels. Genetic factors have been implicated in the aetiology following mutations in a single gene. An extremely rare form of diabetes mellitus is monogenic diabetes, a subset of which is permanent neonatal diabetes, and is usually suspected if a child is diagnosed with diabetes at less than 6 months of age. We present the first case reported from East Africa of a child diagnosed with permanent neonatal diabetes resulting from a mutation in the KCNJ11 gene encoding the Kir6.2 subunit. Despite the rarity of permanent neonatal diabetes, this diagnosis should be considered in infants with persistent hyperglycaemia requiring insulin therapy. Children with an ATP-sensitive potassium channel defect in the pancreatic beta cell have an overall good prognosis when treated with oral sulphonylurea therapy.