The liquid-liquid equilibrium of aqueous solutions of hyperbranched polyesters of generation 2,3 and 4 is described by the lattice-cluster theory. The gist of this approach is the incorporation of the architecture of the polymer directly into the thermodynamic quantities, like Gibbs energy of mixing. The very important geometric parameters describing the polymer architecture are calculated in a new way that seems to be more realistic than older ones. The phase-equilibrium calculations include the binodal curve, the spinodal curve and the critical point neglecting the polydispersity of the polymer samples. Without any additional adjustable parameter these corrections lead to a shift of the cloud-point curve towards higher polymer concentration, as observed in experiments. However, the agreement of the calculated and the experimental values is not quantitative. A possible reason for that may be the disregarding of association effects. (C) 2009 Elsevier B.V. All rights reserved.