Minute pulmonary meningothelial nodules are rare lesions histologically composed of small nests of epithelioid cells located within the interstitium of the lung. These nodules are generally asymptomatic and are usually found incidentally at autopsy or in surgical specimens resected for unrelated causes. The lesions are most often single, although multiple lesions with unilateral involvement of one or even all lobes of the same lung have been described. To our knowledge, cases of meningothelial nodules with disseminated bilateral pulmonary involvement associated with clinical symptoms of restrictive pulmonary disease and radiologic evidence of diffuse reticulonodular pulmonary infiltrates have not been previously documented. We have studied 5 patients presenting with diffuse bilateral pulmonary involvement by numerous minute pulmonary meningothelial nodules. The patients were 4 women and a man aged 54 to 75 years who presented clinically with dyspnea and shortness of breath and the lesions were discovered on open lung biopsies performed for the evaluation of diffuse bilateral interstitial lung infiltrates found on chest x-rays and computed tomography scans. In 3 patients, there was a previous history of malignancy and the radiologic findings were suspected of representing diffuse metastatic disease. Histologically, the lesions were composed of small clusters of epithelioid cells with round to oval nuclei devoid of atypia and surrounded by abundant eosinophilic cytoplasm. Immunohistochemical studies showed positivity of the tumor cells for epithelial membrane antigen and vimentin, and negative staining for cytokeratin, actin, S-100 protein, CD34, chromogranin, and synaptophysin. Electron microscopic examination in 1 case confirmed the ultrastructural features of meningothelial cells, including complex cytoplasmic interdigitations joined by well-developed desmosomes and abundant intracytoplasmic intermediate filaments. The diffuse bilateral involvement of lung parenchyma in the present cases can lead to confusion on clinical and radiologic grounds with a variety of interstitial pulmonary processes, including idiopathic interstitial pneumonia and lymphangitis carcinomatosa. Diffuse pulmonary meningotheliomatosis should be considered in the clinical differential diagnosis of diffuse interstitial pulmonary infiltrates.