The problem of mental deficiency is intimately related to a wide variety of medical disciplines as well as medically related specialties. Discussion of the subject, therefore, may be expected to attack the problem from a wide variety of approaches. This monograph by a leading pediatric psychiatrist is primarily concerned with the practical therapeutic implications of the subject. The classification proposed by Kanner, namely, absolute, relative and apparent mental deficiency, is essentially a prognostic one, useful in determining the possibilities of future community adjustment, and in setting up individualized educational, social and psychiatrically oriented therapeutic programs.