1. A first detailed study, correlating behavioral data with neuropathologic findings in a case of cerebral palsy is presented.2. The psychological development and behavior characteristics of A. C. were investigated by repeated observations, cinema records, and a training program, until his death at the age of 14 years.3. Necropsy showed an uncomplicated lesion of the basal ganglia, of the classic status marmoratus type.4. A tabular summary lists the neuropathological and behavioral findings and brings normal and observed functions into comparison.5. The cinema records of A. C. at 7, 10 and 13 years were subjected to frame by frame analysis to ascertain evidences of pattern in the apparently erratic movements of his double athetosis.6. This cinemanalysis revealed temporal and spatial pattern characteristics similar to those of the spontaneous supine activity and the tonic neck reflex of normal infancy. Eleven comparable pattern phases in A. C. and a normal four weeks old infant are identified and delineated.7. The psychological characteristics of A. C. are interpreted in relation to his autonomic, sensori-motor, intellectual and social behavior. The limitations of motor theories of mental life and of mental growth are pointed out.8. In spite of the paucity and disfigurement of kinesthetic experience, A. C. showed remarkable integration of personality and significant approximations to normal mentality.9. Considerable maturation takes place in unimpaired cerebral areas even when they are cut off from normal tactile motor communications.10. The blemish of behavior patterning is not commensurate with the destruction of the primary sensory and motor mechanisms. Mental growth tends toward an optimum organization.