To provide evidence of large numbers of missed opportunities for early HIV diagnosis we designed a retrospective cohort study linking surveillance data from the South Carolina HIV/AIDS Reporting System to a statewide all payer health care database. We determined visits and diagnoses occurring before the date of the first positive HIV test and medical encounters were categorized to distinguish visits that were likely versus unlikely to have prompted an HIV test. Of the 4117 HIV-positive individuals newly diagnosed between 2001 and 2005, 3021 (73.4%) visited a South Carolina health care facility one or more times prior to testing HIV positive. Of these 3021, 1311 (43.4%) were late testers, and 1425 (47.2%) were early testers. Females were less likely than males to be late testers (odds ratio [OR] 0.55, 95% confidence interval [CI] 0.45-0.68), blacks were more likely than whites to be late testers (OR 1.37, 95% CI 1.10-1.71), and persons 50 years of age and older more likely to be late testers (OR 7.16, 95% CI 3.84-13.37). A total of 78.8% of the 13,448 health care visits for both late and early testers were for health care diagnoses unlikely to prompt an HIV test. These findings underscore the need for more routine HIV testing of adults and adolescents visiting health care facilities in order to facilitate early diagnosis.