1. Nine affected and two unaffected members of five families in which dystrophia myotonica has occurred were studied psychiatrically in conjunction with other detailed clinical and research investigations at the University of Colorado School of Medicine.2. The literature dealing with the personality reactions associated with the disorder is reviewed, and3. The results of the study, which included a history of personality development and activity, mental status, physical and neurological examinations, intelligence testing, tests for thinking disabilities and the Rorschach experiment, are reported and an attempt at interpreting them is made.Abstract Teaser