In routine office practice, primary care physicians see both individuals at risk for HIV infection and those who are already infected. They must be prepared to assess risks of HIV infection in all patients, counsel patients with histories of high-risk behavior about the reasons to be tested for infection, and explain the meanings of both positive and negative test results. The initial medical evaluation of an infected individual should include a history and physical examination to detect early manifestations of HIV infection, basic diagnostic tests, including CD4 counts and a purified protein derivative test, and immunization against potentially preventable infections.