The lungs are a primary target for the opportunistic infections and malignancies affecting those with HIV infection. In the patient whose HIV infection is undiagnosed, PCP is the commonest clue to its presence. Early diagnosis prevents morbidity and mortality. Less commonly, interstitial lung disease and tuberculosis, often "primary" or clinically atypical, will be the clue to underlying HIV infection. Other pulmonary complications are usually a late manifestation of HIV infection, which has usually (but not always) already been diagnosed.