TBB does not allow assessment of the distribution of fibrosis within the lobe and lobule, nor does it allow one to determine whether the process is diffuse. For these reasons, Berbescu et al2 used the combination of patchwork fibrosis, fibroblast foci, and microscopic honeycombing as criteria they considered diagnostic of UIP, and some of their illustrations do show fields that could be UIP. But as the authors acknowledge, none of these findings individually has diagnostic specificity, and even this combination could be the result of a variety of processes, including drug reactions, chronic hypersensitivity pneumonitis, connective tissue diseases, or asbestosis. Pathologically, one could also argue that the combination of only patchwork fibrosis and honeycombing (one of Berbescu’s acceptable combinations for diagnosing UIP) in a small specimen has much lower specificity, and it is now recognized that fibroblast foci, often but not exclusively found in areas of dense fibrosis, occur in other interstitial lung diseases. As a further complication, cases of unequivocal UIP can have focal areas that look like nonspecific interstitial pneumonia10; this problem is readily addressed in surgical lung biopsies but likely to cause tremendous confusion in TBB.