The authors report a case of 48 years old woman with mental retardation, followed for 30 years. She has conduct disorder and during this period we note a large number of self-injuries. She swallowed broken glasses, safety pins and once jumped from a bridge. The impulsiveness of these self-injuries is the main factor; they are not planned self-attempts. Lots of different treatments have been prescribed (neuroleptics, antidepressant serotonin uptake blockers and others) and it is only with the lithium that we could observe a period of 2 years without self-injuries. This case questions about the way of action of the lithium and about a possible specificity in the preventive action on conduct disorder with self-injurious behavior, on this type of patient.