The Mass Analyzed Threshold Ionization (MATI) spectrum of 1,4-dioxane has been collected using a one-photon vacuum-ultraviolet (VUV) excitation scheme that is produced via four-wave difference mixing of two pulsed dye lasers. The ionization potential (IP) is 73062 +/- 4 cm(-1), approximately 575 cm(-1) lower than previously reported values. The vibrational structure seen in the cation ground state agrees very well with the ab initio line positions, as determined by density functional theory calculations. Only vibrations of a(g) symmetry are seen in this spectrum, in line with expectations derived from consideration of orbital symmetries.