BACKGROUND: Epstein-Barr virus (EBV) infection has been associated with fatal pneumonitis in immunocompetent patients. We present a case of fatal adult respiratory distress syndrome caused by EBV infection in a patient with acquired immunodeficiency syndrome (AIDS), to our knowledge the first such reported case, along with a survey of archival autopsy cases to assess baseline expression of EBV in AIDS patients. DESIGN: The case patient's autopsy material was studied exhaustively for infectious agents by culture, histochemistry, and immunohistochemistry, with negative results. Formalin-fixed paraffin-embedded lung, spleen, lymph node, and liver tissue were further studied by in situ hybridization using a probe for EBV early RNA (EBER, Kreatech). The same method was applied to lymphoid tissues from eight other archival AIDS autopsy cases. Case patient tissues were also examined by electron microscopy. RESULTS: Strikingly numerous lymphocytes were positive for EBV early RNA in the case patient's spleen, lymph nodes, and hepatic portal areas. In addition to positive lymphocytes in the lung, EBV-infected pneumocytes were also present. Electron microscopy also demonstrated viral material in lymphocytes and pneumocytes. Of the archival cases studied, only one spleen was found to have rare positive lymphocytes. CONCLUSION: Primary or reactivation EBV infection may represent a previously underreported cause of morbidity and mortality in AIDS patients. Autopsy tissues from AIDS patients do not routinely show overexpression of EBV early RNA by in situ hybridization, making this technique ideal for assessing the contribution of EBV to terminal events in these patients.