Routine military screening identified human immunodeficiency virus (HIV) infection in an asymptomatic dentist who had three prior negative antibody tests. A look-back investigation evaluated the provider and the practice and provided notification, counseling, and HIV testing for patients. Test results were linked to dental procedures categorized by levels of invasiveness. Of 1631 patients tested, all were negative for antibody to HIV. Analysis of 12,164 procedures on 876 patients determined 20.5% of patients had procedures from the highest stratum of invasiveness; 42% had only low-risk exposure. Stratification of the degree of invasive exposure and clinical evaluation of disease stage in the infected health care worker are important in look-back investigations. The early stage of disease in the provider, the adherence to infection control precautions, and the low percentage of invasive procedures may have contributed to the lack of transmission. These results are consistent with current assessment that risk of transmission of HIV during invasive medical procedures is low.