The follow-up study of a patient with permanent diabetes (DM) unrelated to islet cell antibody and anti-insulin antibodies and occurring 10 years after a transient neonatal DM episode is reported. A latent defect in insulin release was proved. It produced transient glucosuria during intercurrent illnesses and permanent hyperglycaemia and a decrease in growth velocity [with high stimulated growth hormone and low insulin-like growth factor I (IGF-I)] at the onset of puberty. After insulin therapy was re-introduced, catch-up growth and normalization of the blood glucose and IGF-I levels were noted.