Rituximab is a chimeric, anti-CD20 monoclonal antibody initially approved for relapsed, refractory indolent B-cell non-Hodgkin's lymphoma (NHL), and is being applied in an increasing variety of clinical scenarios. Most adverse events are due to an infusion-related symptom complex, and severe pulmonary complications are rare. We describe a case of an NHL patient who received rituximab and developed symptomatic, biopsy-proven multinodular bronchiolitis obliterans with organizing pneumonia (BOOP). This is the first reported case of BOOP associated with single-agent rituximab, and along with two other patients we describe, as well as two prior reports of BOOP in NHL patients receiving rituximab-based combinations, strengthens the possibility of a causal relationship. Moreover, these findings suggest that the incidence of BOOP following rituximab therapy may be higher than has been previously appreciated. Physicians utilizing rituximab should be aware of this association given the difficulty of differentiating between presentations of BOOP and neoplastic pulmonary processes.