Lung biopsy often plays a key role in identifying patients with hypersensitivity pneumonia, especially in the absence of a typical history. A 69-year-old woman with a 2-year history of unexplained dyspnea on exertion underwent surgical lung biopsy for diagnosis of diffuse lung disease thought to represent idiopathic pulmonary fibrosis. Her biopsy showed honeycomb change and fibroblast foci suggestive of usual interstitial pneumonia, but also showed areas of cellular interstitial pneumonia with chronic bronchiolitis and a pattern of granulomatous inflammation typical of hypersensitivity pneumonia. The classic features of hypersensitivity pneumonia in surgical lung biopsy are emphasized, including a bronchiolocentric cellular interstitial pneumonia, chronic bronchiolitis, and poorly formed nonnecrotizing granulomas. As illustrated in our patient, sometimes subtle histologic clues are key in separating hypersensitivity pneumonia from usual interstitial pneumonia and other forms of idiopathic interstitial pneumonia. Making the distinction is important given differences in treatment strategies and natural history.