Background: Methemoglobinemia is a condition in which the iron in hemoglobin is oxidized from the ferrous to ferric state, resulting in oxygen desaturation and cyanosis. It can be congenital or acquired, with acquired causes including the ingestion of certain medications or chemical products or infections such as sepsis or gastroenteritis. Case presentation: Herein, we report the case of a young infant who presented with diarrhea and cyanosis and was found to have significant methemoglobinemia which most likely was secondary to severe diarrhea. It was managed successfully with methylene blue, he was diagnosed later as case of food protein induced enterocolitis syndrome. Conclusion: Clinicians should consider profound diarrhea as a potential cause of methemoglobinemia to enhance early intervention.

Keywords: Methemoglobinemia, Cyanosis, Diarrhea, Enterocolitis.