PUBLICLY OPERATED PSYCHIATRIC INSTITUTIONS IN THE 16 STATES OF THE SOUTHERN REGIONAL EDUCATION BOARD AREA WERE STUDIED TO FIND THE PROPORTION OF ALL RETARDED ADMISSIONS AND RESIDENTS WHO WERE IN PSYCHIATRIC HOSPITALS AND THE PROPORTION OF ALL PSYCHIATRIC HOSPITAL ADMISSIONS AND RESIDENTS WHO WERE REPORTED TO HAVE PRIMARY DIAGNOSIS OF MENTAL RETARDATION. DATA INDICATED THAT MOST RETARDED RESIDENTS IN THE YOUNGER AGE GROUPS (UNDER 15) WERE IN FACILITIES FOR THE RETARDED, WHEREAS MOST IN THE OLDER AGE GROUPS (OVER 25) WERE IN PSYCHIATRIC HOSPITALS. THE PROPORTION OF ALL RETARDED PATIENTS WHO WERE IN PSYCHIATRIC HOSPITALS IN MANY CASES WAS SUBSTANTIALLY HIGHER THAN THE PERCENT OF ALL PSYCHIATRIC HOSPITAL RESIDENTS WHO WERE DIAGNOSED AS RETARDED. THIRTEEN PERCENT OF ALL PSYCHIATRIC HOSPITAL RESIDENTS IN THE 16 STATES WERE REPORTED TO HAVE A PRIMARY DIAGNOSIS OF MENTAL RETARDATION. THE PERCENT OF ALL RETARDED PATIENTS DIAGNOSED AS RETARDED INCREASED WITH THE LENGTH OF HOSPITALIZATION (5 PERCENT OF THOSE HOSPITALIZED UNDER 1 YEAR, 18 PERCENT OF THOSE HOSPITALIZED 10 TO 19 YEARS) AS DID THE PERCENT OF ALL RETARDED PATIENTS WHO WERE IN PSYCHIATRIC FACILITIES (25 PERCENT OF THOSE HOSPITALIZED UNDER 1 YEAR, NEARLY 50 PERCENT OF THOSE HOSPITALIZED OVER 20 YEARS). HOWEVER, THE PERCENT OF ALL PSYCHIATRIC HOSPTIAL PATIENTS DIAGNOSED AS RETARDED DECREASED WITH AGE (24 PERCENT AGED 15 TO 24, LESS THAN 10 PERCENT AGED OLDER). THE GREAT MAJORITY OF THE OLDER RETARDED PATIENTS WAS IN PSYCHIATRIC FACILITIES. ONLY A SMALL PROPORTION (AN AVERAGE OF 4 PERCENT) OF CURRENT ADMISSIONS TO PSYCHIATRIC FACILITIES HAD A PRIMARY DIAGNOSIS OF MENTAL RETARDATION. MORE THAN FOUR OUT OF 10 RETARDED ADMISSIONS WENT TO PSYCHIATRIC HOSPITALS WITH THE REMAINING SIX OF THE 10 GOING TO FACILITIES FOR THE RETARDED. THE PERCENT OF ALL ADMISSIONS TO PSYCHIATRIC HOSPITALS WHO HAD A PRIMARY DIAGNOSIS OF MENTAL RETARDATION DECREASED WITH AGE (15 PERCENT UNDER 15 YEARS, ALMOST 0 PERCENT AT 75 AND OVER). HOWEVER, THE PROPORTION OF ADMISSIONS WHO ENTERED PSYCHIATRIC HOSPITALS INCREASED WITH AGE (6 PERCENT UNDER 15, 99 PERCENT AT 75 AND OVER). STATISTICAL EVIDENCE IS PRESENTED IN 11 GRAPHS AND FIVE TABLES. A CLINICIAN'S LOOK AT THE DATA IS ALSO INCLUDED. (JD)