  Theoretical relative ages of galactic globular clusters have recently been
challenged by a semi-empirical relation. It was used to point out that tested
sets of isochrones were unable to reproduce the relation and yield internally
inconsistent relative ages. We find that differential cluster ages derived with
the isochrones by Salaris & Weiss (1998) are reliable and internally
consistent. We also show that this consistency depends on using the lower
absolute ages determined by SW98, which therefore receive more empirical
support. Moreover, we discuss the effect of the clusters absolute age on the
evaluation of their differential ages, and its connection with the question of
their age dispersion.
