  Analysis of broad-band X/$\gamma$-ray spectra of NGC~4151 from
contemporaneous observations by {\it GRO}/OSSE, {\it ROSAT}, {\it Ginga} and
{\it ASCA}, shows that the data are well modelled with an intrinsic spectrum
due to thermal Comptonization. The X-ray spectral index changes from
$\alpha\sim$ 0.4 to 0.7, and temperature stays at about 50 keV. The X-ray
spectrum varies in such a way that it is consistent with the roughly constant
soft $\gamma$-rays, with pivots at $\sim$ 100 keV. The UV/X-ray correlation
observed by {\it EXOSAT} and {\it IUE} can be explained by two specific models
with reprocessing of X-rays by cold matter. The first one is based on reemision
of the X-ray flux absorbed by clouds in the line of sight. The model predicts
no Compton reflection which is consistent with the broad-band spectra. The
second model, assumes reprocessing of X-rays and $\gamma$-rays by a cold
accretion disk with dissipative patchy corona. The homogenous corona model is
ruled out here, since the hardness of the X-ray spectrum implies that the
plasma is photon starved. The accretion disk model predicts Compton reflection
which is only marginally allowed by the observations. Both our models satisfy
the energy balance, and provide a good fit to the X/$\gamma$-rays and UV data.
