THE DATA WERE COLLECTED IN CONJUNCTION WITH A 5-MONTH STUDY IN THE HOSPITAL OF A LARGE MIDWESTERN STATE PRISON FOR MEN. DURING THE LAST MONTH OF THE STUDY'S FIELD WORK PHASE (SEPTEMBER, 1972), A SAMPLE OF 300 INMATES WAS SELECTED FROM A COMPLETE LIST OF INMATES PROVIDED BY THE PRISON ADMINISTRATION. INFORMATION ON CHARACTERISTICS OF THE SELECTED INMATES, CONDITIONS OF IMPRISONMENT, LENGTH OF TIME OF PRISON, HEALTH HISTORIES, THE UTILIZATION OF MEDICAL SERVICES, AND DISCIPLINARY REPORTS WAS SECURED FROM PRISON RECORDS IN BOTH THE HOSPITAL AND THE CLASSIFICATION OFFICE. THESE DATA ARE STUDIED IN RELATION TO INMATE UTILIZATION OF MEDICAL SERVICES. RESULTS SHOWED A HIGHER THAN AVERAGE RATE OF MEDICAL CARE UTILIZATION AMONG PRISON INMATES, COMPARED WITH THE GENERAL POPULATION OF U.S. SICK CALLS WERE MORE LIKELY AMONG THE YOUNG, BLACK INMATES, AND THOSE WHO HAD BEEN IN PRISON A RELATIVELY SHORT PERIOD OF TIME, THOSE WHO HAD A HISTORY OF MEDICAL CARE PRIOR TO IMPRISONMENT, AND THOSE WHO INHABITED LESS DESIRABLE ACCOMMONDATIONS IN THE PRISON. THE FINDINGS PARALLEL A SIMILAR STUDY OF PERSONNEL ON NAVAL SHIPS. SEVERAL EXPLANATIONS OF THE UTILIZATION FINDINGS WERE EXPLORED, INCLUDING DISEASE RATES, STRESS, SOCIALIZATIONS, ADMINISTRATIVE POLICY, AND LABELING. TO VARYING DEGREES, A PLAUSIBLE CASE COULD BE BUILT FOR CAUSAL RELATIONSHIPS INVOLVING ALL THESE FACTORS, WITH THE EXCEPTION OF DISEASE RATES. STUDIES DESIGNED TO DIRECTLY MEASURE THESE FACTORS IN COMBINATION ARE INDICATED. TABULAR DATA AND REFERENCES ARE PROVIDED.