Neonatal diabetes mellitus (NDM) is a very rare disorder and its diagnosis can be challenging especially in mild and transient cases. Herein, we describe a 2.4-kg female infant born at 38 wk of gestation who showed hyperglycemia (388 mg/dL) on Day 1. Intermittent blood sampling showed glucose concentrations of 100-150 mg/dL on Day 2-5. However, continuous glucose monitoring (CGM) from Day 7 revealed hyperglycemia (> 200 mg/dL) after every feeding. The patient required low-dose (0.1-0.2 U/kg/d) insulin therapy for a short period (7 d). During the treatment, hypoglycemic (< 50 mg/dL) events were not detected by real- time CGM. Follow-up CGM from Day 32 showed normoglycemia for 3 full days; therefore, we ascertained that the diabetes had been transient. Later genetic analysis revealed an abnormal methylation pattern on chromosome 6q24, which is the most frequent cause of transient NDM. Most cases of 6q24-related NDM relapse after puberty, implying that long term follow up is required. We speculate that the NDM in this case might not have been diagnosed without CGM. This report highlights the usefulness of CGM for the initial diagnosis, monitoring during insulin therapy, and confirmation of improvement in patients with transient NDM.