Measurements of molar enthalpy increments for {0.5 H2O + 0.5 (CH3)(2)CO} are reported. A counter-current water-cooled flow calorimeter was used to measure 113 enthalpy increments over the temperature range 373.2 K to 573.2 K at pressures from 0.1 MPa up to 12.0 MPa. Extrapolation of the gas phase measurements to zero pressure gave values in excellent agreement with the mean of the pure component ideal gas enthalpies calculated from spectroscopic data. The boundary of the two-phase region was constructed with the aid of data derived from (vapour + liquid) equilibrium measurements. Enthalpies of flash vaporisation of the mixture at x = 0.5, obtained from the boundaries of two-phase region, lie nearly midway between the enthalpies of vaporisation of the pure components.