When we grouped patients from small town/rural areas and micropolitan towns together and compared them to metropolitan patients, the prevalence of depression was greater in rural patients (CD4 counts < 200 cells/mm3, 55.0 vs. 40.0%, P = 0.073; CD4 counts 200–350 cells/mm3, 60.9 vs. 34.8%, P = 0.002; and, CD4 counts > 350 cells/mm3, 54.4 vs. 43.2%, P = 0.033). The gene discussed is CD4; the disease is major depressive disorder.