The purpose of the present experiment is to elucidate the abnormal behaviors in the blind that are commonly grouped under the heading of "blindisms". The so-called blindisms was defined in this paper as the stereotyped behavior of a blind person. The study was divided into four parts. In the first part of this study the phenomenon of stereotypy was mainly analyzed by behavioral observation. The examiner stood in the front of a dayroom or a schoolroom and recorded the behaviors of subjects for a period of 45 minutes every Sunday at the same time of the day. The subjects were 16 blind cases of severe mental retardation (from 6 to 25 years of age) and 30 blind cases with normal intelligence (from 4 to 36 years of age). The second part of the study was concerned with the diurnal variation of the appearance of blindisms in 24 hours. recorded by the examiner's observation and by memo-motion camera (Fujica single 8). The subjects were 18 blind cases of severe mental retardation, three cases of amblyopia and a blind subject with normal intelligence. The third part of the study was a statistical analysis on the relationship between age and appearance rate of blindisms, and comparison of appearance rate of blindisms between blind subjects with normal intelligence and blind subjects with severe mental retardation. The subjects with normal intelligence were divided into four age groups. (1) 30 preschool and elementary school children (4 to 11 years of age), (2) 23 middle school children (12 to 14 years of age), (3) 21 high school students (15 to 17 years of age) and (4) 19 adult subjects (over 18 years of age). The fourth part of the study was a comparison between blindisms and the stereotyped movements of subjects with other sensory disturbances. The subjects were 12 deaf subjects with severe mental retardation and 21 blind subjects with severe mental retardation.It was found that blindisms in the blind with severe mental retardation and those in the blind with normal intelligence had two common features: (1) repetition and continuation of a set of stereotyped behaviors (2) accompaniment of fine rhythmic repetitive movements. The basic principles of these features were rhythmicity, repetitiveness, preservation of steady individual pattern of stereotyped behaviors. The mode of the stereotyped behaviors can be classified into two types: (1) simple type, which is characterized by repetitive and rhythmic movement of a part of a motor organ, and (2) synchronous type, which is characterized by complex repetitive synchronous movements of various motor organs of the whole body. An example of a simple type behavior is head-rolling, and that of a synchronous type is rubbing hand with body-rocking and twirling of feet at the same time. In addition to these phenomenological characteristics, starting of the stereotyped behaviors was sudden, without any motive or aim, and even the subject himself was unaware of his own stereotyped movements. In the second part of the study on the variation of blindisms for twenty-four hours the following observations were made: (1) the tendency of blindisms behavior to continue over an hour, (2) the presence of two peaks in the appearance of blindisms behaviors, at 9-10 o'clock and around 13 o'clock, and (3) the presence of individual pattern of diurnal variation of blindisms behaviors. The results of the third part were as follows: (1) No statistical difference among four age-groups were observed concerning the appearance rate of blindisms. On the other hand, significant difference was found on the appearance rate between subjects with complete blindness and subjects with amblyopia within three age-groups of pre-school and elementary school children, middle school children and high school students (p<0.05). Significant difference between subjects with congenital complete blindness and subjects with acquired complete blindness was observ

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