The myelopathy and neuropathy associated with chronic misuse of nitrous oxide are potentially reversible if the habit is discontinued. This occurred in each of the reported cases, including our case, when it was transiently discontinued. Although a causal relationship between nitrous oxide and this myelopathy-neuropathy has not been proved, the circumstantial evidence is convincing. Both physicians and dentists should be aware of this potentially serious complication of chronic self-administration of nitrous oxide, especially in persons inclined to misuse drugs. Dentists, with their access to nitrous oxide, may be particularly at risk.