Over the last decade state prisons have experienced unprecedented growth and many demographic changes. At the same time, courts are requiring states to provide mental health screening and treatment to prisoners. Findings from recent studies indicate that the prevalence of mental illness is higher in prisons than in the community, and comorbidity is common. Our ability to generalize from these studies is limited, however, because of major shifts in the demographic mix in prisons during the past decade. New studies on the prevalence of mental illness in prisons, which consider these recent changes would help planners allocate funds and staff to more effectively meet the needs of these individuals.