Common complications of thoracic radiotherapy include esophagitis and radiation pneumonitis. However, it is important to be aware of uncommon post-radiotherapy complications such as bronchiolitis obliterans organizing pneumonia (BOOP). We report on two patients with carcinoma of the breast who developed an interstitial lung disease consistent with BOOP. BOOP responds to treatment with corticosteroids and the prognosis is generally good despite of the need for long-term administration of corticosteroids as relapses can occur during tapering of steroids. This report provides guidelines for the evaluation and treatment of patients with pulmonary infiltrates after radiotherapy.