Negative health consequences of illicit drug use, such as cardiovascular complications and infectious diseases, increase the likelihood of the need for health care. However, evidence suggests that, with the exception of emergency services, drug users generally are medically underserved. Furthermore, the effect of illicit drug use on health care utilization is becoming an especially important issue for the criminal justice system, because an increasing proportion of inmates in correctional institutions have a history of drug use. This 1998–1999 study of 661 incarcerated men in the Kentucky prison system focused on predictors of unmet physical, behavioral, and overall health care needs among chronic substance users. Analyses revealed that White incarcerated drug users were more likely to report unmet physical and overall health care needs than non-Whites and those with high school education or above were more likely to report unmet physical, behavioral, and overall health care needs. In addition, more episodes of serious illness, more mental health problems, and poorer self-rated health were predictive of all three types of unmet health care needs. A longer career of drug use emerged as a significant predictor of unmet behavioral health care needs, whereas more frequent drug use in the year before incarceration predicted unmet physical health care needs. Further research directions and implications for in-prison health care planning are discussed.