Bronchoalveolar lavage is a useful diagnostic tool in diffuse or disseminated lung malignancies that do not involve the bronchial structures visible by endoscopy. The neoplastic histotype and the intraparenchymal neoplastic growth pattern are good predictors for diagnostic yield; adenocarcinoma, and tumors with lymphangitic or lepidic growth patterns are more easily diagnosed by bronchoalveolar lavage; in these cases the diagnostic yield reported is higher than 80%. In hematologic malignancies the diagnostic yield is quite good in secondary diffuse indolent B cell lymphomas and in primary B cell lymphomas of mucosa-associated lymphoid tissue (MALT) type but low in Hodgkin disease. Morphological analysis may be implemented by immunocytochemical or molecular tests to identify the cell lineage and the presence of monoclonality. Disorders in which bronchioloalveolar cell hyperplasia/dysplasia is a significant morphological component may have cytological features in bronchoalveolar lavage fluid that mimic lung neoplasms: acute respiratory distress syndrome (ARDS), acute interstitial pneumonitis (AIP), and acute exacerbation of idiopathic pulmonary fibrosis are the most important clinical entities in this group.