DISCUSSION: Diffuse alveolar hemorrhage is a documented side effect of treatment with antithyroid medications, albeit a rare one. A literature review demonstrated two documented cases of methimazole induced diffuse alveolar hemorrhage. In the case reported above, infectious studies including fungal culture, bacterial culture, viral panel, influenza, acid fast stain, and KOH stain were negative. Autoimmue workup, as is customary in cases of DAH, including MPO-ANCA, were also negative. The previous two reported cases of MMI induced DAH were associated with MPO-ANCA positivity.