In patients with AIDS, isolation of cytomegalovirus (CMV) from respiratory secretions is common. It is often found with other pathogens, which has led to debate regarding its role as a primary pulmonary pathogen. A retrospective investigation of patients with AIDS and CMV as a sole pulmonary isolate was performed in an attempt to describe their clinical presentation and course. All patients admitted to the hospital with pneumonia and with BAL or transbronchial biopsy (TBB) specimen positive for CMV between 1991 and 1994 were identified through a review of inpatient records. Inclusion criteria included positive CMV cultures from BAL, cytomegalic inclusion bodies from BAL or TBB, and thorough documentation of the absence of other pulmonary pathogens. Nine patients met the inclusion criteria for CMV pneumonitis. Seven were male and two were female, ages 26 to 44 years, and all had a history of opportunistic infections. Typical clinical presentation was characterized by increased respiratory rate, hypoxemia, and diffuse interstitial infiltrates. The mean CD4 count was 29.6 (±22) cells per cubic millimeter, mean lactate dehydrogenase level was 414 (±301) IU/L, and in seven patients in whom CMV antigen was measured it was greater than 50 positive cells per 200,000 WBCs. Three untreated patients died of respiratory failure and three had autopsy confirmation of CMV pneumonia. Five patients were treated with anti-CMV therapy for at least 2 weeks, and all demonstrated improvement in symptoms, oxygen saturation, and chest radiograph. At 3 months follow-up, all five patients were asymptomatic with no pulmonary symptoms. At 6 months follow-up, three of the five patients remained asymptomatic; the other two died of other opportunistic infections. In at least these nine patients, CMV represented a primary pulmonary pathogen. Patients who were treated responded quickly and were able to be discharged home from the hospital with marked improvement in their symptoms. We recommend that clinicians consider this diagnosis in the proper setting and consider treatment with anti-CMV therapy.