Bronchiolitis obliterans organizing pneumonia (BOOP) is a pathologic finding common to various injuries to the lung of either definite or idiopathic etiology. Since the presentation of patients with idiopathic BOOP varies, we studied 16 patients with BOOP on pulmonary histology to define more distinct and homogeneous clinical and imaging profiles of idiopathic BOOP. We distinguished three groups of patients: group 1 (n = 4), with multiple patchy migratory pulmonary involvement of the pneumonia type. Their clinical course was subacute, with cough, fever, weight loss, mild dyspnea, and increased ESR. Chest x-ray film and CT scan showed multiple alveolar opacities. All patients completely recovered with corticosteroid therapy but relapsed when therapy was stopped too rapidly. Group 2 (n = 5) had solitary pulmonary involvement of the pneumonia type occurring in a similar clinical context. Since carcinoma was suspected, they underwent surgical excision of the pneumonic area and recovered without relapse. Group 3 patients (n = 7) presented with diffuse pulmonary involvement of the interstitial lung disease type. They had more progressive onset of more severe dyspnea, crackles heard over all lung surfaces, and interstitial opacities with or without alveolar opacities on chest imaging. Improvement with corticosteroid therapy was obtained in only three patients. In all three groups, lung function test results showed a restrictive pattern. The obstructive pattern characteristic of pure bronchiolitis obliterans was found in none. BAL showed a mixed pattern (increase of both lymphocytes and polymorphonuclear cells) in the patients of the first two groups. Thus, we distinguished three characteristic clinical and imaging profiles in patients with idiopathic BOOP: multiple patchy pneumonia, solitary pneumonia, and diffuse interstitial lung disease. These profiles are so different that they should be distinguished in clinical studies of idiopathic BOOP.