The benzaldehyde nitrone moiety in the title molecule, N-benzylidene-4-fluoroaniline N-oxide, C13H10FNO, like that in N-(benzylidene)methylamine N-oxide [Bed-ford, Chaloner and Hitchcock (1991). Acta Cryst. C47, 2484-2485] approaches planarity [C-benz-N=C-C-benz 179.5 (5) and C-benz-C-benz-C=N -13(1)degrees cf 176.0 (2) and 6.8 (2)degrees, respectively, in the methyl compound]. However, the p-fluorobenzene substituent is substantially twisted out of the molecular plane [C-benz-C-benz-N=C -42.8 (8)degrees] in order to avoid a non-bonded O ... H. clash.