Congenital Diaphragmatic Hernia (CDH) is a defect in the development of the diaphragm in which abdominal viscera herniate into the chest resulting in pulmonary hypoplasia and hypertension. A common treatment strategy to reach physiologic stability before surgical repair is the use of inhaled Nitric Oxide (iNO). This usage of iNO can result in methemoglobinemia as seen in a female newborn that was born with a right CDH and was started on iNO on the second day of life. We saw an uptrend in methemoglobin to 3.3% with an increase in lactate to 7.5 which was counteracted with a blood transfusion and weaning off the iNO which successful maintained her at physiologic status until her CDH could be repaired at day 9 of life. The general guidelines on how to treat methemoglobinemia secondary to iNO shows that asymptomatic patients can be treated with weaning alone and those with moderate symptoms can be treated with methylene blue. In our patient with a high lactic acidosis and rapidly increasing methemoglobin levels, an exchange transfusion was indicated.