Free-breathing non-contrast enhanced 1H MRI techniques show promise as a surrogate for ventilation imaging but more validation against methods which directly image lung ventilation is needed in patients. The aim of this work was to investigate the relationship between 1H free-breathing and 3He breath-hold ventilation images in patients with CF. Phase-resolved functional lung (PREFUL) 1H and 3He ventilation images were compared in 10 patients with CF. Qualitative similarities were observed between techniques to varying degrees. Ventilation defect percentage showed strong correlation between methods and with FEV1, although median and inter-quartile range fractional ventilation values were not related.