MRI is increasingly used in radiotherapy treatment planning due to its superior soft tissue contrast. The growing interest in 3T MRI relates to the potential of higher signal-to-noise ratio and spatial resolution. However, geometric distortions associated with magnetic field inhomogeneity increase with field strength and may compromise geometric accuracy. We quantify the geometric distortion in MRI examinations for high dose rate brachytherapy planning for gynaecological cancer at 3T, and consider its clinical impact, taking into account the brachytherapy applicators, the subject’s susceptibility distribution and hardware-related distortions. We found localised areas of field inhomogeneity, and displacements of less than 1mm.