The clinical utility of bronchoalveolar lavage fluid (BAL) cell analysis for the diagnosis and management of patients with interstitial lung disease (ILD) has been a subject of debate and controversy. The American Thoracic Society (ATS) sponsored a committee of international experts to examine all relevant literature on BAL in ILD and provide recommendations concerning the use of BAL in the diagnosis and management of patients with suspected ILD. To provide recommendations for (1) the performance and processing of BAL and (2) the interpretation of BAL nucleated immune cell patterns and other BAL characteristics in patients with suspected ILD. A pragmatic systematic review was performed to identify unique citations related to BAL in patients with ILD that were published between 1970 and 2006. The search was updated during the guideline development process to include published literature through March 2011. This is the evidence upon which the committee's conclusions and recommendations are based. Recommendations for the performance and processing of BAL, as well as the interpretation of BAL findings, were formulated by the committee. When used in conjunction with comprehensive clinical information and adequate thoracic imaging such as high-resolution computed tomography of the thorax, BAL cell patterns and other characteristics frequently provide useful information for the diagnostic evaluation of patients with suspected ILD.