Three cases of manic-depressive illness in mentally retarded adults.

The authors point out that manic-depressive illness is often not diagnosed in mentally retarded patients because they are already regarded as "different." They discuss the use of lithium carbonate as a prophylactic agent in the treatment of manic-depressive illness in mentally retarded patients and present three case histories illustrating some of the difficulties encountered in diagnosing mania or hypomania in such patients. They provide a number of suggestions to help physicians recognize and treat these disorders.