Chronic necrotizing pulmonary aspergillosis (CNPA) is an indolent, cavitating process in the lungs resulting from invasion of lung tissue by Aspergillus spp. However, most previous reports have not found any clear evidence of parenchymal invasion, and clinical distinction between CNPA and chronic cavitary pulmonary aspergillosis (CCPA) is difficult. We performed a histopathological study of lung specimens obtained by autopsy, surgical resection, or biopsy to clarify the characteristic pathological and clinical features of CNPA. We present 4 cases of proven CNPA, diagnosed by histological demonstration of tissue invasion by the fungus, and present its clinical features. These 4 patients were male, and the mean age was 62 years (range, 51-75 years). Their underlying conditions were chronic obstructive pulmonary disease (n = 3), sequelae of pulmonary tuberculosis (n = 2), and diabetes mellitus (n = 1). Aspergillus precipitation tests were positive for 3; and Aspergillus antigen tests were positive for 2 on admission, and subsequently, for all 4. The isolated pathogens were Aspergillus niger for 1 and A. fumigatus for 1. Initial radiographic findings were infiltrates or nodular lesions, which slowly progressed and cavitated before the appearance of fungus balls. Although CNPA has characteristic pathological features, it is clinically difficult to distinguish CNPA from CCPA. We propose to use the term chronic progressive pulmonary aspergillosis for both CNPA and CCPA.