Hodgkin's lymphoma is commonly treated with a combination of chemotherapy drugs including doxorubicin, bleomycin, vinblastine, and dacarbazine. Antibody-drug conjugates such as brentuximab vedotin are now being used to treat Hodgkin's lymphoma that has not responded to standard treatment. Brentuximab vedotin is a monoclonal antibody that selectively delivers a cytotoxic agent, monomethyl auristatin E, which targets cells expressing surface CD30 markers, a protein that may be found in high amounts in some cancer cells including lymphoma cells. Common adverse effects of the drug include diarrhea, nausea, anemia, and fatigue. We present a case of a patient with diabetic ketoacidosis and profound insulin resistance secondary to brentuximab. Diabetic ketoacidosis is a rare but serious adverse reaction in this growing class of antibody-drug conjugates.