The crystal structure of Cs 2[VOF 4(H 2O)] has been studied on the basis of three-dimensional neutron and X-ray diffraction data. The structure is orthorhombic; a = 15.251(2), b = 6.486(1), and c = 7.010(1) Å; Z = 4; V = 693.46 Å 3; space group Ccmm (No. 63). From the neutron data the positions of all atomic species except vanadium were refined. The final R w value was 0.030 for 427 independent reflections with σ(I) I ⩽ 0.60 . In the X-ray case the positions of nonhydrogen atoms were refined. The final R w value was 0.022 for 509 observations with σ(I) I ⩽ 0.40 . The structure contains strongly deformed octahedral complex ions [VOF 4(H 2O)] 2−, held together by hydrogen bonds OHF (forming chains in the c direction) with cesium atoms inserted between them. The vanadyl ion VO 2+ (VO) bond distance 1.602(8) Å; X-ray value) is coordinated to four fluorine ligands and to one H 2O molecule in trans position to the vanadyl oxygen. The VF and the VO w distances are 4 × 1.919(4) and 2.268(8) Å, respectively; all are X-ray values. The OH distance is 0.987(7) Å and the HO w H angle 105.1(9)°. The coordination numbers of the two crystallographically independent cesium atoms are 13 and 11, respectively.