ONE SAMPLE STUDIED CONSISTED OF 247 VOLUNTEER INMATES AT A PRISON. FOR EACH INMATE A DETAILED HOUSING AND MEDICAL HISTORY THAT COVERED A MINIMUM OF THE LAST 6 MONTHS WAS EXAMINED. ALL ILLNESS COMPLAINTS EXCEPT COLDS, FLU, AND COMPLAINTS THAT COULD NOT BE CONSTRUED AS FACILITATED BY STRESS, WERE EMPLOYED IN THE ANALYSIS. THE MOST FREQUENT CATEGORIES OF COMPLAINTS WERE BACKPAIN, NAUSEA, RASH, SINUS, CONSTIPATION, CHEST PAIN, AND ASTHMA. OF THE 247 VOLUNTEERS, ONLY 64 OF THEM MET THE CRITERION OF HAVING LIVED A MINIMUM OF 30 DAYS IN EITHER A DORMITORY SETTING (26 OR MORE INMATES) OR A SINGLE OR TWO-PERSON CELL. ILLNESS COMPLAINT RATE FOR A GIVEN PERIOD OF TIME WAS DEFINED AS THE NUMBER OF DAYS IN WHICH ONE OR MORE COMPLAINTS WERE RECORDED IN THE MEDICAL HISTORY, DIVIDED BY TOTAL DAYS. ILLNESS COMPLAINT DATA FROM THE COUNTY JAIL WAS IN THE FORM OF WRITTEN REQUESTS FOR MEDICAL ATTENTION SUBMITTED BY INMATES. THE NUMBER OF THESE WRITTEN REQUESTS AS WELL AS THE SOCIAL AND SPATIAL DENSITY OF THE HOUSING UNITS WERE OBTAINED FOR 5 CONSECUTIVE WEEKS. THE TOTAL POPULATION OF THE JAIL DURING THIS PERIOD RANGED FROM 824 TO 885, AND THE TOTAL NUMBER OF MEDICAL REQUESTS WAS 776. WITH REGARD TO THE PRISON, ILLNESS RATES WERE CALCULATED FOR SUBJECTS IN ALL THREE SAMPLES WHO WERE HOUSED FOR A MINIMUM OF 30 DAYS IN EITHER A DORMITORY SETTING OR SINGLE-PERSON AND TWO-PERSON CELLS. A T-TEST COMPARISON OF ILLNESS COMPLAINT RATES IN THE DORMITORY AND THE SINGLE AND DOUBLE CELLS YIELDED A SIGNIFICANTLY GREATER ILLNESS COMPLAINT RATE IN DORMITORY SETTINGS. BY MEASURING ILLNESS RATE DURING THE FIRST 30 DAYS OF DORMITORY HOUSING IN COMPARISON WITH THE RATE DURING THE LAST 14 TO 30 DAYS OF SUCH HOUSING, IT WAS CONCLUDED THAT STRESS MANIFESTED IN SICKNESS WAS NOT DUE TO THE FACTOR OF INITIAL PRISON ADJUSTMENT. IT IS CONCLUDED, THEREFORE, THAT HIGH SOCIAL DENSITY AND/OR SPATIAL DENSITY INDUCES STRESS THAT, LIKE OTHER STRESSORS, CAN INCREASE THE RATE OF ILLNESS COMPLAINTS. THE DATA GATHERED FROM THE COUNTY JAIL, WHICH IS MORE CROWDED THAN THE PRISON, ARE CONSIDERED TO SUBSTANTIATE THE FINDINGS OF THE PRISON STUDY. TABULAR DATA AND REFERENCES ARE INCLUDED.