The title compound, C(4)H(12)NO(3) (+)·CHO(2) (-), was obtained from 1,3-dihy-droxy-2-(hy-droxy-meth-yl)propan-2-aminium acetate and ethyl formate. In the crystal, the cations and anions are held together by inter-molecular N-H⋯O and O-H⋯O hydrogen bonds.