We studied the histological and clinicopathological findings in 42 patients who had lymphomatoid granulomatosis (LYG). In addition to small round lymphocytes, small to intermediate lymphocytes with serpentine nuclei, large immature mononuclear lymphoid cells, abundant histiocytes, and vascular invasion by the cell infiltrate were observed in all cases. Fifty percent of lesions had occasional "atypical" cells with multi-lobed nuclei. Three of four follow-up autopsies showed large cell lymphoma, while one other autopsy and the single repeat biopsy showed increased numbers of large immature mononuclear lymphoid cells. Patients were most frequently men 40-60 yr old who had a history of pulmonary symptoms, such as cough or chest pain, and who showed multiple bilateral lung nodules without hilar adenopathy in the chest x-ray. Thirteen patients (38%) died of disease, 11 of them within 12 mth of initial diagnosis. The presence of neurological signs and symptoms, increased mitoses, or increased numbers of atypical multi-nucleated cells in the initial biopsy were not statistically significant predictors of survival.