Neonatal diabetes mellitus (NDM) is a monogenic form of diabetes mellitus that occurs in the first 6 months of life. It is a rare condition with a prevalence of 1 in 100,000–500,000 live births. We report a 3-month-old girl child with high blood glucose levels. She was diagnosed with diabetes mellitus during the 28th day of life and was on treatment with insulin. She was admitted for the control of high blood glucose levels during which she was started on multiple daily insulin treatment, but the control had been poor. As the age of onset is <6 months of life, genetic analysis has been done. It revealed the presence of a heterozygous mutation p. Gly334Val (p. G334V) in KCNJ11 gene which confirmed the diagnosis of NDM. The child was successfully shifted from insulin to sulfonylureas, and the blood glucose levels are well maintained.