The ATP-sensitive K channel controls insulin secretion from the islet. Mutations in KCNJ11 can cause permanent and transient neonatal diabetes. To date, more than 30 KCNJ11 mutations have been revealed as related to the onset of neonatal diabetes mellitus (NDM), most of which are responsive to glibenclamide treatment. In the present study, we sequenced the KCNJ11 gene in a Chinese girl diagnosed with NDM and in her parents. An in-frame 15-bp KCNJ11 deletion was identifi ed in the patient, whereas no KCNJ11 deletions were found in her parents, indicating that this deletion was de novo. The patient was responsive to the treatment of glibenclamide. Ten months of follow-up showed that, besides permanent NDM, the motor and intelligence development of the girl was normal and she suffered no onset of convulsions. The result, to some degree, improved our knowledge on NDM. © 2013 by Walter de Gruyter.