This case study describes a 34-year-old woman presenting with a subacute history of dyspnoea associated with pleural based masses and pulmonary infiltrates. A computed tomography guided biopsy confirmed the presence of a pleural based thymoma, and a video assisted thoracoscopic lung biopsy revealed the pulmonary infiltrates to be a lymphocytic interstitial pneumonitis (LIP). The thymomas responded successfully to chemotherapy and the LIP improved following corticosteroid therapy.