<i>Aim:</i> To determine the timing of the peak cortisol response to the insulin hypoglycaemia (IH) test in children and to establish paediatric reference data. <i>Methods:</i> We retrospectively reviewed all IH tests in a tertiary paediatric endocrine referral centre over a 6-year period. Inclusion criteria were age <16 years and adequate hypoglycaemia (glucose ≤2.0 mmol/l). Patients with an impaired hypothalamic-pituitary-adrenal axis or receiving glucocorticoid medication were excluded. Fifty-four subjects (35 males) met the criteria. Blood samples were collected at –30, 0, 20, 30, 60, 90, 120, and 150 min in relation to insulin bolus injection (0.15 U/kg) at 0 min. Glucose, cortisol, and growth hormone (GH) were measured in all samples. <i>Results:</i> Peak cortisol and GH responses occurred by 90 min in all subjects. Peak cortisol was inversely correlated with age (r<sub>s</sub> –0.65, p < 0.0001). The median (5th centile) peak cortisol value was 689 nmol/l (547 nmol/l) in children younger than 10 years as compared with 555 nmol/l (468 nmol/l) in those older than 10 years (p < 0.0001). Peak cortisol was not related to peak GH (r<sub>s</sub> –0.20, p = 0.15). <i>Conclusions:</i> Blood sampling in the IH test may be curtailed 90 min after injection. The peak cortisol response to IH is age related.