Anti-androgen therapy is commonly used for prostate cancer and it has been reported to induce severe hyperglycemia. Diabetic chorea is characterized by acute uni- or bilateral chorea or ballismus and hyperintensity of the striata on T1-weighted magnetic resonance imaging (MRI) images, and is associated with changes in the blood glucose level. We report here a case of diabetic chorea caused by severe hyperglycemia induced by anti-androgen therapy. A 71-year-old man received a diagnosis of prostate cancer and was given leuprorelin acetate (11.25mg, every 3 months) and bicalutamide (80mg/day). After the third injection of leuprorelin acetate, he developed involuntary movements of the right extremities. His glucose and hemoglobin A1c levels were found to be markedly elevated (691mg/dl and 19.5%, respectively), and brain MRI showed high-intensity areas in the left striatum on T1-weighted imaging. The diagnosis was diabetic chorea and he was admitted to our department. His involuntary movements diminished immediately after intravenous infusion of 500 ml saline. His blood glucose level was decreased after initiation of basal/bolus insulin therapy and discontinuation of leuprorelin acetate, but he gradually developed involuntary movement of right extremities again.