Diffuse pulmonary hemorrhage denotes a diffuse bleeding into the alveoli as a result of severe damage of the alveolocapillary membrane. Autoimmune diseases, toxic injury and hemodynamic changes are the most frequent causes. A 45 year old male patient presented with diffuse alveolar hemorrhage. An Immunoglobulin A (IgA) paraprotein secreting myeloma was found to be the underlying cause. Immunohistochemistry revealed dense pericapillary and perivascular deposits of IgA, indicating a paraprotein mediated damage of the alveolocapillary membrane. The predominantly vascular pattern of damage was regarded as the most likely cause of the pulmonary hypertension in this patient. The diffuse pulmonary bleeding stopped after initiation of treatment consisting of vincristine, adriamycine and dexamethasone.