We describe a patient with extranodal (pulmonary) marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) who was refractory to treatment with cytotoxic chemotherapy. After a single four-week course of rituximab she had significant regression of pulmonary lesions and remains progression free 19 months after finishing her treatment. This case report demonstrates the potential efficacy of rituximab as a single therapeutic agent in patients with pulmonary MALT lymphoma.