Diffuse panbronchiolitis (DPB) is a chronic inflammatory disease of the airways with a high rate of mortality despite treatment with a combination of antibiotics and the use of supportive therapy such as oxygen administration. Low-dose erythromycin therapy (EM) (400 to 600 mg/d) has been found to improve the survival of patients with DPB, and most patients with DPB in Japan have been treated with this erythromycin regime since 1984. The purpose of this study was to evaluate the effects of treatment with erythromycin on the survival rate of patients with DPB in Japan. We compared the survival rates of 498 patients with DPB after dividing them into three groups according to the date of their first medical examination (Group a: 1970-1979, Group b: 1980-1984, Group c: 1985-1990). DPB had been diagnosed in these patients using the criteria of the Ministry of the Health and Welfare Diffuse Lung Disease Committee (MHW-DLDC), which includes chronic productive cough, shortness of breath, presence of roentgenologically smoldering symmetrical granular shadows in the middle and lower lung fields, limitation of airflow without decrease in DLCO, elevated serum cold hemagglutinin titers, and/or narrowing bronchiolus with infiltration of lymphocytes and foamy alveolar macrophages. These patients were registered in the DPB research group of the Ministry of Health and Welfare (MHW). Survival rates were statistically compared using the generalized-Wilcoxon test. The survival rate of Group c was significantly higher than that of Groups a (p < 0.0001) and b (p < 0. 0001). In Group c, eight of 87 patients died; five died in the EM nontreated subgroup (n = 24), and three died in the EM-treated subgroup (n = 63). There was a significant difference in the survival rates between the two subgroups in Group c (p < 0.001). Treatment with EM was associated with a significant improvement in the rate of survival of patients with DPB. The efficacy of EM treatment increased the survival rate of patients with DPB, which was more significant in the older than in the younger patients.