The study is concerned with the cognitive development of mentally retarded young persons. These persons are compared with a control group, including a replication after three years. Cognitive development measures digit span ( wais ) / embedded figures test / Gibson spiral maze / Benton visual retention test / STM cross modal coding task / matching familiar figures test / Torrance test / divergent thinking task / Cotan norms / iq-tests / family-life / games / socialization techniques. Background variables: basic characteristics/ residence/ occupation/employment/ education/ social class