Here we describe a case of subacute combined spinal cord degeneration caused by nitrous oxide (N2O, laughing gas) use. Because of its euphoric effects, the use of N2O has become increasingly popular in recent years. Unfortunately, the use of N2O leads to inactivation of vitamin B12. Vitamin B12 plays an essential role in the synthesis and maintenance of myelin, a fatty substance that surrounds nerve cells and is crucial for their functioning. Deficiency of vitamin B12 could typically result in degeneration of posterior and lateral columns of the spinal cord. Treatment with intramuscular vitamin B12 injections and abstinence of N2O generally leads to gradual improvement of symptoms. Our case demonstrates the importance of the methyl malonic acid test to detect early or mild vitamin B12 deficiency as a cause of myelopathy while serum vitamin B12 level may be normal. Written consent was obtained from our patient to publish the details of this individual case.