We have determined the crystal structure of a bovine enterovirus, revealing that the topologies of the major capsid proteins and the overall architecture of the virion are similar to those of related picornaviruses. The external loops joining beta-strands are truncated and the canyon region is partially filled by an extension of the VP3 G-H loop giving the viral capsid a relatively smooth appearance. These changes may have implications for cell attachment. In spite of these differences the virus maintains a hydrophobic pocket within VP1, occupied by a specific 'pocket factor' which appears to be myristic acid. These observations support the proposal that a kinetic equilibrium exists between occupied and unoccupied pocket states, with occupation inhibiting uncoating.