Context.-Surgical removal and pathologic handling of lung tissue has a compressive effect upon its architecture. The effect of surgical atelectasis on morphology has not been examined in depth, especially with respect to lung adenocarcinomas. Objective.-To examine the influence of surgical atelectasis on morphologic lepidic growth pattern, mimicking papillary adenocarcinoma pattern. Design.-In 2 cases serial sections of resected pulmonary adenocarcinoma were used, as was a 3-dimensional reconstruction. Elastin stains were performed on primary and metastatic adenocarcinomas. Results.-Perfusion fixation of another case showed marked morphologic differences of less compressed peripheral lung tissue, emphasizing the preexisting alveolar structure. An elastic stain may help identify true lesional architecture. Conclusions.-We demonstrate that microscopic sections of adenocarcinoma in situ in compressed/collapsed tissue may give rise to a pseudopapillary pattern mimicking invasive adenocarcinoma. Accurate appreciation of different tumor architecture in lung adenocarcinoma has important biologic and clinical implications. Pathologists should be aware of the possibility of misclassification of adenocarcinoma pattern due to tissue artifacts caused by lung tissue handling.