A new international statement defines usual interstitial pneumonia (UIP) which is a histological and radiological form of idiopathic pulmonary fibrosis (IPF) more precisely than previously. In the diagnosis of IPF, either in high resolution computed tomography (HRCT) a UIP pattern must be present or alternatively specific combinations of HRCT and surgical lung biopsy findings can be accepted. In about two third of the cases IPF can be diagnosed by clinical and radiological criteria. Thus surgical lung biopsy is needed in about one third of cases to achieve the ultimate diagnosis, which requires multidisciplinary cooperation. In large clinical trials conducted during the last decade, lung biopsy was performed in about 30-60% of the cases. The most serious complication of lung biopsy is mortality within 30 days after the procedure, with a frequency of about 3-4% reported in most studies. Because of the histological variability, surgical lung biopsy should be taken from a minimum of two lobes. The number of fibroblast foci in surgical lung biopsy has been shown to correlate with survival in several studies.