Previous data on sulfur diffusion in single crystal CdTe has been expanded to include the more practical example of diffusion in polycrystalline CdTe thin films. Samples of vacuum evaporated CdTe were sealed, with a source of sulfur vapour, in evacuated silica ampoules and annealed at temperatures of either 372, 450 or 550 degreesC for times up to 28 days. Sulfur diffusion profiles were measured by secondary ion mass spectrometry. A new method to correct for finite film thickness was used to determine the grain boundary diffusion coefficients. These show that films grown at high temperatures, such as those produced by close-space sublimation, may possess sulfur enriched grain boundaries that extend through the complete thickness of the CdTe film. However, extensive decoration of the grain boundary by hexagonal CdSxTe1-x is believed unlikely. (C) 2003 Elsevier Science B.V. All rights reserved.