Bronchoalveolar lavage (BAL) has gained widespread acceptance as a procedure that can be performed safely to retrieve respiratory secretions for the examination of cellular and acellular components for both diagnostic and research purposes [1–6]. When BAL was initially developed as a tool to sample respiratory secretions in animal models of lung disease and subsequently adapted as a clinical tool to study interstitial lung disease (ILD), it was perceived as holding considerable promise for the diagnosis and management of various forms of ILD, such as sarcoidosis, idiopathic pulmonary fibrosis (IPF) and hypersensitivity pneumonitis (HP). Indeed, hundreds of articles have been published in the medical literature over the ensuing decades as various centres around the world began to use BAL to identify agents of respiratory infections and examine correlates of changes in the composition of the airspace milieu associated with the presence of noninfectious parenchymal lung diseases. BAL is now routinely used as a tool to diagnose respiratory infections, evaluate patients with acute respiratory failure or evidence of diffuse parenchymal lung diseases, and monitor the status of transplanted lung allografts [7]. Despite the widespread use of BAL by pulmonologists, BAL cellular analysis, especially nucleated immune cell differential counts, may be underused in ILD diagnosis. Information derived from BAL appearance and differential cell counts can provide useful diagnostic clues if recognised and interpreted appropriately with an adequate awareness of the potential diagnoses that are associated with specific BAL cellular patterns.