The diagnosis of lymphangioleiomyomatosis was established in a 35-year-old woman with hemoptysis, mild cough, and dyspnea based on histologic review of results of a transbronchial biopsy correlated with high-resolution computed tomographic scan findings. A chest x-ray film revealed diffuse interstitial lung disease, and a high-resolution computed tomographic scan showed diffuse cystic changes throughout both lungs. The transbronchial biopsy specimen revealed cystic changes and a patchy, sometimes nodular proliferation of smooth muscle that focally expanded the interstitium suggestive of lymphangioleiomyomatosis. The smooth-muscle nature of the cells was confirmed by positive immunohistochemical stains for actin and desmin; positive staining for HMB-45 was also observed. Although the diagnosis of lymphangioleiomyomatosis usually requires an open lung biopsy, this case shows that rarely, in the appropriate clinical setting, the diagnosis may be rendered based on results of a transbronchial biopsy in conjunction with findings from ancillary immunohistochemical studies and high-resolution computed tomography.