The present invention relates to a method for preparation a glycolide polyester by ring opening polymerization characterized in that glycolide monomer with optional co-monomer(s) of cyclic ester(s) is/are subjected to ring opening polymerization in the presence of a dispersion stabilizer and a catalyst, said catalyst being selected for precipitating glycolide homopolymer or copolymer from solvent, said solvent being selected so that the glycolide monomer and the optional co-monomer(s), the dispersion stabilizer and the catalyst are soluble therein but said glycolide homopolymer or copolymer is non-soluble. The present invention further relates to an in situ ring opening polymerizing process product, and to use of said glycolide polyester, and to further processing of said glycolide polyester.