  We analyze the mass of the axino, the fermionic superpartner of the axion, in
general supergravity models incorporating a Peccei--Quinn--symmetry and
determine the cosmological constraints on this mass. In particular, we derive a
simple criterion to identify models with an LSP--axino which has a mass of
$O(m_{3/2}^2/f_{PQ})=O($keV) and can serve as a candidate for (warm) dark
matter. We point out that such models have very special properties and in
addition, the small axino mass has to be protected against radiative
corrections by demanding small couplings in the Peccei--Quinn--sector.
Generically, we find an axino mass of order $m_{3/2}$. Such masses are
constrained by the requirement of an axino decay which occurs before the
decoupling of the ordinary LSP. Especially, for a large Peccei--Quinn--scale
$f_{PQ}>10^{11}$ GeV this constraint might be difficult to fulfill.
