Neonatal diabetes mellitus is a rare clinical condition, which develops most commonly secondary to mutations in KCNJ11 and ABCC8 genes encoding ATP-sensitive K+ channels. Patients are typically diagnosed with hyperglycemia-related symptoms in the first 6 months of life and rarely with ketoacidosis. In this article, we report an infant who presented with focal clonic convulsion and thereafter was diagnosed with neonatal diabetes mellitus and thrombi in cerebral venous sinus. In this patient, after a molecular analysis of the ABCC8 gene revealed a novel heterozygous missense mutation (p.D424V), a successful transition from insulin to sulfonylurea treatment was made.