BACKGROUND: The number of immunocompromised hosts has been increasing steadily and a new pulmonary infiltrate in these patients a potentially lethal condition which needs rapid diagnosis and treatment. In this study we sought to examine the clinical manifestations, radiologic findings, and therapeutic outcomes of pulmonary mycoses presenting as a new pulmonary infilrate in immunocompromised hosts. METHOD: All cases presenting as a new pulmonary infilrate in immunocompromised hosts and confirmed to be pulmonary mycoses by pathologic examination or by positive culture from a sterile site between October of 1996 and April of 1998 were included in the study and their chart and radiologic findings were retrospectively reviewed. RESULTS: In all, 14 cases of pulmonary mycoses from 13 patients(male : female ratio = 8 : 5, median age 47yr) were found. Twelve cases were diagnosed as aspergillosis while two were diagnosed as mucormycosis. Major risk factors for fungal infections were chemotherapy for hematologic malignancy (10 cases) and organ transplant recipients(4 cases). Three cases were receiving empirical amphotericin B at the time of appearance of new lung infiltrates. Cases in the hematogic malignancy group had more prominent symptoms : fever(9/10), cough(6/10), sputum(5/10), dyspnea(4/10), chest pain(5/10). Patients in the organ transplant group had minimal symptoms(p<0.05). On simple chest films, all of the cases presented as single or multiple nodules (6/14) or consolidations(8/14). High resolution computed tomograph showed peri-lesional ground glass opacities(14/14), pleural effusions(5/14), and cavitary changes(7/14). Definitive diagnostic methods were as follows : 10 cases underwent minithoracotomy, 2 underwent video-assisted thoracoscopic surgery, 1 underwent percutaneous needle aspiration and 1 case was diagnosed by culture of abscess fluid. All cases received treatment with amphotericin B with 1 case each being treated with liposomal amphotericin B and itraconazole due to renal toxicity. Lung lesion improved in 12 of 14 patient but 4 patients died before completing therapy. CONCLUSION: When a new lung infiltrate develops presenting either as a nodule or consolidation in a neutropenic patient with hematologic malignancy or in a transplant recipient, you should always consider pulmonary mycoses as one of the differential diagnosis. By performing aggressive work up and early treatment, we may improve prognosis of these patients.