[Delusion of mercury poisoning in multiple sclerosis].

We confirmed the diagnosis of multiple sclerosis in a 54-year-old man. The patient rejected this diagnosis and was completely convinced that all his symptoms resulted from a chronic mercury intoxication. We found evidence that this delusional disorder was an independent illness, and not a "symptomatic psychosis in multiple sclerosis." So far, little notice has been taken in psychiatry of delusions of environmental poisoning, which cause difficulties in applying common criteria of delusion.