The aim of this paper is to present a three-year observation of four children with permanent neonatal diabetes caused by heterozygous activating mutations in both KCNJ11 gene for Kir6.2 and ABCC8 gene for SUR1 subunits (three patients after three years of clinical observation and one patient after two years of clinical observation, respectively). In three cases with Kir6.2 mutation, developmental delay was diagnosed. In all four patients the glucagon test revealed normal c-peptide secretion. During the treatment with sulfonylureas (SU), glycaemia remained within the normal range, HbA1c<7%, in our patients. In all children reduction a of SU doses was required.