Few pharmacological approaches for the treatment of obesity exist at this time, and most of them are unsatisfactory, whereas this disease is widespread both in the developed and developing world. Novel effective approaches are needed for the development of antiobesity agents possessing different mechanisms of action. A possible new approach for the treatment and prophylaxis of obesity is based on the inhibition of carbonic anhydrases (CAs, EC 4.2.1.1), enzymes involved in several steps of de novo lipogenesis, both in the mitochondria and the cytosol of cells. Topiramate and zonisamide are two antiepileptic drugs that were shown to induce persistent weight loss in obese patients, but their mechanism of action is largely unknown. We demonstrated strong CA inhibitory properties for these two drugs, by means of kinetic studies in solution and X-ray crystallography, against several physiologically relevant isoforms, such as CA II, VA and VB. It has been proved that topiramate also inhibits lipogenesis in adipocytes, similarly to other sulfonamide CA inhibitors investigated earlier. A large number of new sulfonamides have been synthesized and assayed as possible inhibitors of CA isoforms involved in lipogenesis. This is the beginning of a very new and promising approach for the treatment of obesity, with the hope that new compounds showing this property will be soon developed and available for clinical use.