The authors report 10 patients with a distinctive idiopathic bronchiolocentric interstitial pneumonia having some histologic similarities to hypersensitivity pneumonitis. Bronchiolocentric interstitial pneumonia has a marked predilection for women (80%) and occurs in middle age (40-50 years). Chest radiographs and pulmonary function tests show interstitial and restrictive lung disease, while the histologic appearance is that of a centrilobular inflammatory process with small airway fibrosis and inflammation that radiates into the interstitium of the distal acinus in a patchy fashion. Granulomas are not identified. At a mean followup of approximately 4 years in nine patients, 33% of patients were dead of disease and 56% had persistent or progressive disease suggesting a more aggressive course than hypersensitivity pneumonitis and nonspecific interstitial pneumonia, the two major disease processes in the differential diagnosis. Whether Bronchiolocentric interstitial pneumonia is a unique entity or not, the pattern of bronchiocentric injury to the lung in the absence of known causes and its clinical presentation as interstitial lung disease, warrants further investigation of this unusual interstitial process.