  We discuss the non-self-averaging phenomena in the critical point of weakly
disordered Ising ferromagnet. In terms of the renormalized replica
Ginzburg-Landau Hamiltonian in dimensions D <4, we derive an explicit
expression for the probability distribution function (PDF) of the critical free
energy fluctuations. In particular, using known fixed-point values for the
renormalized coupling parameters, we obtain the universal curve for such PDF in
the dimension D=3. It is demonstrated that this function is strongly
asymmetric: its left tail is much slower than the right one.
