The effect of synchrobetatron coupling on the dynamic aperture was studied by comparing the dynamic aperture for a particle with a large fixed &Dgr;p/p, no synchrotron oscillations present, with the dynamic aperture for a particle, with a synchrotron oscillation amplitude of the same &Dgr;p/p. The particle with the synchrotron present was found to have a smaller dynamic aperture than the particle with the fixed &Dgr;p/p. It is suggested that this reduction in dynamic aperture may be due to non‐linear coupling between the longitudinal and transverse motions. (AIP)