In the cystal structure of the title compound, (2-hy-droxy-ethyl)trimethylammonium dihydrogen phosphate, C(5)H(14)NO(+)·H(2)PO(4) (-), two anions create dimeric structures via two O-H⋯O hydrogen bonds. The hydrogen-bonded dimers are connected by another O-H⋯O hydrogen bond with the hydroxyl groups of the cations, constructing a columner structure along the a axis. A number of C-H⋯O interactions are also present.