In this talk I will present recent simulations of Primordial Black Hole (PBH) formation in a cosmological scenario described by a single perfect fluid, eventually including a cosmological constant. These results will clarify different aspects of PBH scenario that were unclear so far. Using a time independent curvature perturbation on a super horizon scale, it is possible to obtain a first order quasi homogeneous solution that describes initial conditions self consistent with pure growing solutions of cosmological perturbations as one expects are raising from inflation. The scaling law profile of the mass spectrum is characterised by the critical collapse phenomenon which turns out to be a crucial aspect of PBHs. The hydrodynamic collapse is characterized by the formation of a strongly evacuated region around the black hole that, after the formation of the black hole, is gently refilled by the outside cosmological fluid, leading to a very stable state of the PBH, slowly accreting. The simulations seems to show that this final state of a single PBH is well approximated by a stationary solution that can be connected to an expanding FRW universe. The PBHs formed in this context gives important informations about the history of the early universe and are also excellent candidates for objects like: cold dark matter, solar mass objects like MACHOS, intermediate mass black holes and seeds of the super massive black holes observed in the centre of galaxies.