Diagnostic studies of a series of 159 pre-school retarded children are reported with a focus on the disturbances in emotional development. It is emphasized that mental retardation is a clinical developmental syndrome which regularly includes an impairment in emotional as well as in intellectual development. Psychological characteristics which are more closely related to the degree of retardation than to any other diagnostic factor are termed the primary psychopathology of the mental retardation syndrome. The primary psychopathology is described and illustrated in terms of the developmental disturbance and special descriptive traits. Points of differential diagnosis are discussed.Abstract Teaser