We analyzed the prevalence of chronic illnesses, including mental illness, and access to health care among US inmates. We used the 2002 Survey of Inmates in Local Jails and the 2004 Survey of Inmates in State and Federal Correctional Facilities to analyze disease prevalence and clinical measures of access to health care for inmates. Among inmates in federal prisons, state prisons, and local jails, 38.5% (SE = 2.2%), 42.8% (SE = 1.1%), and 38.7% (SE = 0.7%), respectively, suffered a chronic medical condition. Among inmates with a mental condition ever treated with a psychiatric medication, only 25.5% (SE = 7.5%) of federal, 29.6% (SE = 2.8%) of state, and 38.5% (SE = 1.5%) of local jail inmates were taking a psychiatric medication at the time of arrest, whereas 69.1% (SE = 4.8%), 68.6% (SE = 1.9%), and 45.5% (SE = 1.6%) were on a psychiatric medication after admission. Many inmates with a serious chronic physical illness fail to receive care while incarcerated. Among inmates with mental illness, most were off their treatments at the time of arrest. Improvements are needed both in correctional health care and in community mental health services that might prevent crime and incarceration.