The aim of this study is to evaluate the clinical course and prognosis of stable IPF patients over the first 12 months. A retrospective observational study was conducted in the patients with IPF proved by surgical lung biopsy between May 1995 and April 2010 at Samsung Medical Center in Korea. The patients were classified into stable or progressive IPF by analyzing the clinical, physiologic, and radiologic data. One hundred twelve patients were stable during the first 12 months. Mean age was 61 years and 79 (70.5%) patients were male. Ninety three patients (83%) were progressive and 19 (17%) patients were stable at least for 3 years. During 4 years of follow-up, 20 (17.9%) patients died and acute exacerbation occurred in 11 (9.8%)patients. Multivariate logistic regression model revealed that extent of parenchymal abnormalities of chest computed tomography (CT) scan at the time of diagnosis was independently associated with progression of stable IPF patients for the first 12 months follow-up (Odds ratio=1.34; 95% confidence interval=1.02 to 1.78, p=0.04). Although IPF patients are stable for the first 12 months, most patients experience progression, and progression is more salient in patients with increased extent of parenchymal abnormalities of CT scan at the time of diagnosis.