The upper critical solution temperature (UCST) and lower critical solution temperature (LCST) have been predicted for 45 polymer/solvent systems based on Patterson＇s theory. The configurational energy and configurational heat capacity used in the theory are determined by the following thermodynamic relations -U-conf. = gamma(V)TV C-P,C- (conf.) = alpha(P)T gamma(V)V where the thermal expansion coefficient and thermal pressure coefficient are obtained from our empirical equations ln(alpha(P)T)(-1) = 1.1820 + 0.8425 ln (T-C-T/T) ln(gamma(V)/gamma(VC)) = 0.8452 +/- 1.1324 ln(V/V-C) + 2.8940[ln(V/V-C)](2) where T-C, V-C and gamma(VC) are the critical temperature, critical volume and thermal pressure coefficient at the critical state. The deviations between predicted and experimental UCST and LCST are generally less than 20 degrees C for 28 polymer/solvent systems. The molecular weight dependence of UCST and LCST is predicted for polystyrene (PS)/cyclohexane, PS/methyl cyclohexane and PS/toluene systems, and good agreement with experimental results is obtained.