OBJECTIVE The purpose of our study was to compare the findings seen on HRCT with those from pathologic examination in patients with diffuse micronodular lung disease (DMLD). METHODS Forty consecutive patients with biopsy-proven DMLD (each nodule being <5 mm in diameter and occupying more than two-thirds of lung volume on chest radiograph) were included. High resolution CT (HRCT) scans were analyzed with particular attention to the location of nodules in and around the secondary pulmonary lobule (centrilobular, perilymphatic, and random) and the zonal distribution. The findings were compared to pathology. RESULTS CT scans showed centrilobular nodules in the patients with diffuse panbronchiolitis (n = 4), infectious bronchiolitis [n = 4; Hemophilus influenzae (n = 3) and Mycoplasma pneumoniae (n = 1)], hypersensitivity pneumonia (n = 3), bronchogenic disseminated tuberculosis (n = 3), pneumoconiosis (n = 1), primary lymphoma of the lung (n = 1), and foreign body-induced necrotizing vasculitis (n = 1). They demonstrated perilymphatic nodules in the patients with pneumoconiosis (n = 5), sarcoidosis (n = 2), and amyloidosis (n = 2). They demonstrated micronodules of random distribution in the patients with miliary tuberculosis (n = 9) and pulmonary metastasis (n = 5). Upper and middle zonal predominance was seen in two of two patients with sarcoidosis and in two of six patients with pneumoconiosis. The CT location of nodules in the secondary pulmonary lobule represented the location and nature of the lesion on pathologic examination. CONCLUSIONS By showing the distribution of micronodules in and around the secondary pulmonary lobule, HRCT enables the narrowing of the differential diagnosis of DMLD. CT findings reflect gross morphologic features of pathologic examination.