Vapor-liquid equilibrium (VLE) measurements have been performed for cyclohexene-isophorone and cyclohexanol-isophorone binary systems at 101.3 kPa. The L-W test method confirmed the thermodynamic consistency of the experimental VLE data for the binary systems. These data are compared to theoretical predictions by COSMOtherm and overall show good agreement. Due to the success of the COSMOtherm predictions, theoretical data for the cyclohexene-cyclohexanol-isophorone ternary system is obtained.