[en] It is shown that general relativity is important both qualitatively and quantitatively for interpreting the observed parameters of X-ray bursters. Stringent upper limits for the radius and mass of a neutron star are obtained. These follow from combining the value of the average observed peak temperature in the burst (blackbody spectrum assumed) together with the requirement that the luminosity does not exceed the local critical luminosity. The limits contradict the values obtained from calculations of neutron star models, which are larger by a factor of (>=)3.5. The low values of mass and radius arise solely from general relativistic effects. The contradiction can be removed if the burst luminosity is highly non-isotropic or if static equilibrium in the surface layers (which is assumed in He flash models) is rejected. (author)