Neonatal diabetes mellitus (NDM) is a very rare disease defined as hyperglycemia that occurs during the first month of life, requires insulin treatment, and lasts more than 2 weeks. There are 2 types of NDM: permanent neonatal diabetes mellitus (PNDM) and transient neonatal diabetes mellitus (TNDM). We report a case of PNDM in a 3-day-old female infant. This full-term neonate was born small for gestational age. Respiratory distress, poor activity, hypothermia, poor feeding, dehydration, and ketoacidosis were noted at the age of 3 days. After insulin therapy and fluid replacement, her condition became stable. Glucagon test done at the age of 26 days showed serum C-peptide level to be low for her age. During the first year of life she had catch-up growth, but insulin therapy was still required. Serum C-peptide level was undetectable at the age of 15 months. The course of this case indicates the importance of a high index of suspicion for patients with PNDM in order to correct metabolic derangement as early as possible and facilitate normal growth and development under insulin therapy.