Topiramate is effective in migraine headache prophylaxis. Pulmonary symptoms are rarely described as adverse effects. We report the case of a 42-year-old woman with migraine headaches who developed chronic shortness of breath while taking topiramate. Our patient experienced hand paresthesiae at a dose of 25 mg daily, and exercise induced dyspnea at doses above 50 mg daily; these symptoms worsened with increasing topiramate doses. Physical exam and chest x-ray were normal. Blood gas revealed a metabolic acidosis. Symptoms resolved after discontinuation of topiramate. Topiramate induces a lowering of blood carbon dioxide, which is usually asymptomatic. This is due to inhibition of carbonic anhydrase at the proximal renal tubule resulting in impaired proximal bicarbonate reabsorption. The decrease in CO(2) blood level facilitates the occurrence of metabolic acidosis. To our knowledge, this is the first case report of topiramate-induced dyspnea in a patient with migraine headaches.