The histopathologic pattern provides the most important prognostic marker for idiopathic interstitial pneumonia; however, studies have suggested that short-term changes in lung function may be more important. We investigated the prognostic factors for fibrotic interstitial pneumonia. The clinical features and follow-up course of 179 patients (131 with idiopathic pulmonary fibrosis and 48 with nonspecific interstitial pneumonia; 41 fibrotic types and 7 cellular) were analyzed retrospectively. The lung function indices improved or stabilized in most patients with fibrotic nonspecific interstitial pneumonia in contrast to the deterioration or stable condition of most patients with idiopathic pulmonary fibrosis. The 5-year survival of patients with fibrotic nonspecific interstitial pneumonia (76.2%) was better than for those with idiopathic pulmonary fibrosis (43.8%) (p = 0.007). Multivariate analysis at the time of presentation revealed that pathologic pattern, age, and diffusion capacity had important prognostic implications. However, after 6 months of follow-up, changes in FVC, initial diffusion capacity, and sex were the only independent prognostic factors, with no additional prognostic information conferred by the histologic diagnosis. Our data confirmed the importance of physiological parameters including short-term change in FVC. However, at the time of diagnosis, histopathology was important for the prediction of prognosis and future change in lung function.