A 26-year-old man with a one-year history of asthma and sinusitis presented with bilateral pleural effusions, patch basilar infiltrates on a chest x-ray and a pericardial effusion on an echocardiogram. The peripheral blood showed marked eosinophilia. An obstructive pattern was also observed during the pulmonary fuction test, which was responsive to bronchodilator inhalation. Nerve conduction studies showed right sural neuropathy. Thoracentesis yielded an acidotic exudative effusion with low glucose, low C3 and eosinophilia. An open lung biopsy revealed an eosinophilic interstitial pneumonitis associated with a necrotizing eosinophilic vasculitis, and granulomatous inflammation foci. In the literature, pleural effusions were reported in 29 percent of Churg-Strauss patients, but the number of effusions was low and their characteristics have not been well described. This report describes the characteristic findings of pleural fluid and its histologic features in a case of classical Churg-Strauss syndrome.