Voltage-gated sodium channels initiate electrical signaling in excitable cells and are the molecular targets for drugs and disease mutations, but the structural basis for their voltage-dependent activation, ion selectivity, and drug block is unknown. Here, we report the crystal structure of a voltage-gated Na+-channel from Arcobacter butzleri (NavAb) captured in a closed-pore conformation with four activated voltage-sensors at 2.7 Å resolution. The arginine gating charges make multiple hydrophilic interactions within the voltage-sensor, including unanticipated hydrogen bonds to the protein backbone. Comparisons to previous open-pore potassium channel structures suggest that the voltage-sensor domains and the S4-S5 linkers dilate the central pore by pivoting together around a hinge at the base of the pore module. The NavAb selectivity filter is short, ~6.5 Å wide, and water-filled, with four acidic side-chains surrounding the narrowest part of the ion conduction pathway. This unique structure presents a high field-strength anionic coordination site, which confers Na+-selectivity through partial dehydration via direct interaction with glutamate side-chains. Fenestrations in the sides of the pore module are unexpectedly penetrated by fatty acyl chains that extend into the central cavity, and these portals are large enough for the entry of small, hydrophobic pore-blocking drugs.