Theoretical calculations of positron lifetimes, affinities and core electron contributions to Doppler broadening spectra are carried out for several phases (polymorphs) of SiO2. An interesting feature of SiO2 is that not all polymorphs have the same coordination of Si and O atoms, which also affects positron properties. The calculated quantities are compared with available experimental data and discussed with reference to SiO2/Si interfaces. (C) 2002 Elsevier Science B.V. All rights reserved.