Nonspecific interstitial pneumonitis (NIP) and lymphocytic interstitial pneumonitis (LIP), with or without lymphocytic alveolitis, are poorly understood pulmonary complications of HIV infection. These disorders probably represent a spectrum of lymphoproliferative processes that overlap, rather than distinct illnesses. The clinical presentation, radiographic findings, and physiologic abnormalities in NIP and LIP are not specific and therefore require a biopsy for definitive diagnosis. The clinical course of these illnesses is generally favorable, even without specific treatment.