Whereas the majority of researchers accept the important role of shocks in accelerating particles at the Sun and in the heliosphere, there remain many details to be determined. In this paper the sizes of coronal shocks required by prompt solar particle events are compared with sizes of interplanetary shocks determined frominsitumeasurements. Energetic particle observations imply the existence of shocks extending at least 300° whereas interplanetary shocks at 1 AU extend at most about 180°. The observations can be understood if the longitudinal extents of shocks evolve as they propagate outwards from the Sun. ©1996 American Institute of Physics.