  We investigate the stability of Higgs potential in inverse seesaw models. We
derive the full two-loop RGEs of the relevant parameters, such as the quartic
Higgs self-coupling, taking thresholds into account. We find that for
relatively large Yukawa couplings the Higgs quartic self-coupling goes negative
well below the Standard Model instability scale $\sim 10^{10}$ GeV. We show,
however, that the ``dynamical'' inverse seesaw with spontaneous lepton number
violation can lead to a completely consistent and stable Higgs vacuum up to the
Planck scale.
