To predict the natural history of pulmonary Mycobacterium avium-intracellulare (MAI) infection with nodular bronchiectasis, we retrospectively evaluated clinical manifestations, laboratory data, and bronchoalveolar lavage fluid (BALF) findings in 57 patients. The patients received follow-up chest computed tomographic scans and testing for sputum bacteriology between intervals of at least 12 mo. They were divided into two groups after observation for 28 +/- 13 mo: deteriorated (n = 34) and not-deteriorated (n = 23). There were no patients with spontaneous improvement. At the start of observation, the mean age was greater in the deteriorated group (69 +/- 9 yr) than in the not-deteriorated group (57 +/- 9 yr). The mean body-mass index was lower in the deteriorated group (19.2 +/- 3.1 kg/m(2)) than in the not-deteriorated group (21.5 +/- 1.5 kg/m(2)). C-reactive protein, erythrocyte sedimentation rate, and carbohydrate antigen 19-9 were significantly elevated in the deteriorated group. The BALF findings of the deteriorated group showed that the neutrophil cell counts were significantly increased. Thirty-four of 57 patients with pulmonary MAI infection with nodular bronchiectasis had progressive clinical and/or radiographic disease. The older and thinner patients tended to become worse. Neutrophil-related inflammation associated with a decrease in CD4+ lymphocyte might reflect the progression of pulmonary MAI infection with nodular bronchiectasis.