  We study the free energy distribution function of weakly disordered Ising
ferromagnet in terms of the D-dimensional random temperature Ginzburg-Landau
Hamiltonian. It is shown that besides the usual Gaussian "body" this
distribution function exhibits non-Gaussian tails both in the paramagnetic and
in the ferromagnetic phases. Explicit asymptotic expressions for these tails
are derived. It is demonstrated that the tails are strongly asymmetric: the
left tail (for large negative values of the free energy) is much more slow than
the right one (for large positive values of the free energy). It is argued that
in the critical point the free energy of the random Ising ferromagnet in
dimensions D<4 is described by a non-trivial universal distribution function
being non self-averaging
