Hydrothermally synthesized LiFePO4 has been prepared with different synthesis times in order to study defects in the crystal structure and their evolution. The Mössbauer spectra can be interpreted as due to three components, Fe2+ in LiFePO4, Fe2+ in unreacted precursor material which resembles the Mössbauer spectrum of Fe2+ in vivianite (Fe3(PO4)2·8H2O) and Fe3+. The Fe3+ contribution differs from room temperature oxidation of the precursor material, and can partly be due to charge compensating defects in the LiFePO4 structure. With increasing synthesis time, the latter two contributions virtually disappear from the spectra.