Objectives: To identify mutations in the ABCCB and KCNJ11 genes and to evaluate cognitive and motor development and glycemic control in patients with CHL Methods: A prospective study was conducted on 2 cases with CHI diagnosed and treated in National Hospital of Pediabic from March 2010 to May 2010. Results: No mutations welC' found in the KCNJ11 gene. Mutations in ABCCB: were detected in 2 patients with severe CHL In the first case, a compound heterozygote for two missense mutations, F686I (which is a newly discovered mutation) from her father (c.2056TA) and F686S from her mother (c.2057TC) of the ABCCB gene was identified. Second case was identified with a compound heterozygote for F686S mutation from his father and a novel point mutation in the splice donor site of exon-intronjunction, IVS27-1GA !Tom his mother in the ABCCB gene. Both patients were unresponsive to medical treatment with diazoxide and they underwent total pancreatectomy. After 24-28 month follow-up, both of them achieved stable blood glucose levels, normal psychomotor development Condusions: CHI unresponsive to medical treatment with diazoxide is usally associaled with mutation in ABCC8 gene. Near total pancreatectomy is necessary for patients unresponsive to medical treatment The patient need to be followed up in terms of blood glucose level and cognitive and motor development.