[Page 803]Major depressive disorder (MDD) is termed a serious mental illness and has a 12-month prevalence of approximately 7% in the United States. The prevalence of MDD in prison populations is slightly higher, with the condition affecting approximately 10% of incarcerated males and 12% of incarcerated females, although some studies report rates as high as 25% in prison populations. The World Health Organization has predicted that MDD will be the most problematic disease in the world in the 21st century. Despite this, there is little research regarding treatment of MDD in prison populations. This entry begins with a brief discussion of the hallmark symptoms of MDD and then moves to discussions of diagnosis/assessment, etiology/course, treatment, and adjustment to prison life, particularly as it relates to ...