Voltage-gated sodium channels mediate regenerative inward currents that are responsible for the initial depolarization of action potentials in brain neurons. Many of the most widely used antiepileptic drugs, as well as a number of promising new compounds suppress the abnormal neuronal excitability associated with seizures by means of complex voltage- and frequency-dependent inhibition of ionic currents through sodium channels. Over the past decade, advances in molecular biology have led to important new insights into the molecular structure of the sodium channel and have shed light on the relationship between channel structure and channel function. In this review, we examine how our current knowledge of sodium channel structure-function relationships contributes to our understanding of the action of anticonvulsant sodium channel blockers.