In 2006, CDC recommended human immunodeficiency virus (HIV) testing for adults, adolescents, and pregnant women in health-care settings and HIV testing at least annually for persons at high risk for HIV infection* to foster early detection, facilitate linkage to care, and improve health outcomes. Understanding previous HIV testing patterns among persons recently diagnosed with HIV infection can help in the design of HIV testing strategies that reduce the time between onset of HIV infection and its diagnosis. To assess previous HIV testing patterns among adults and adolescents newly diagnosed with HIV infection, CDC analyzed data for the period 2006-2009 from 18 jurisdictions participating in HIV incidence surveillance through CDC's National HIV Surveillance System (NHSS).† This report describes the results of that analysis, which indicated that among adults and adolescents for whom testing history information (THI) was available, 41% were diagnosed with HIV infection at their first HIV test, and 59% had a negative test at some point before HIV diagnosis. Groups with the highest percentage of persons testing HIV-negative ≤12 months before HIV diagnosis included those aged 13-29 years (33%), males with HIV transmission attributed to male-to-male sexual contact (29%), and whites (28%). These results demonstrate that many persons diagnosed with HIV infection have never been tested previously. Persons who are unaware of their HIV infection might not change their behavior to reduce the risk for transmission and will not be linked to care, resulting in worse health outcomes. Enhanced efforts are needed to increase annual HIV testing for populations at high risk for HIV infection to increase early detection.