Osmotic demyelination syndrome refers to the myelin destruction of various brain structures that follows Osmotic stress. It affects myelinated brain; therefore, it is very rare in babies and it has not been reported in patients younger than 10 months of age. Herein, we present a 40-day-old infant with osmotic demyelination syndrome, along with imaging findings. Her Pontine and thalamic lesions regressed during the 10-day treatment course, whereas demyelinated areas in the lentiform nucleus persisted. Magnetic resonance spectroscopy of the latter revealed decreased levels of all major metabolites. Imaging findings remained unchanged after that phase.