OBJECTIVE Whereas prison inmates are reported to exhibit poorer overall health status and higher rates of health care utilization than the general population, no current information exists on the overall disease profile of the U.S. prison population. The present study examined the prevalence of major acute and chronic conditions in one of the nation's largest prison populations. METHODS The study population consisted of 170,215 Texas Department of Criminal Justice (TDCJ) inmates who were incarcerated between August 1997 and July 1998. Information on medical conditions and sociodemographic factors was obtained from an institution-wide medical information system. RESULTS Infectious diseases (29.6%) constituted the most prevalent major disease category among inmates. This was followed by diseases of the musculoskeletal system and connective tissue (15.3%), diseases of the circulatory system (14.0%), mental disorders (10.8%), and diseases of the respiratory system (6.3%). Among the specific conditions examined, evidence of tuberculosis infection without active pulmonary disease (20.1%) was found to be the most prevalent condition, followed by hypertension (9.8%), asthma (5.2%), low back pain (5.1%), and viral hepatitis (5.0%). CONCLUSIONS The present study shows that for a number of conditions, the prison population exhibited prevalence rates that were substantially higher than those reported for the general population. Moreover, estimates for a number of diseases varied substantially according to age, race, and gender. Understanding the disease profile in U.S. incarcerated populations will permit correctional administrators to develop more efficient health care delivery systems for prison inmates.