The total vapor pressures of thulium. trilialides TmCl3, TmBr3, and TmI3 were measured by the torsion method, and their temperature dependence can be expressed by the following equations over the given temperature ranges: TmCl3(cr), log(p/kPa) = (11.60 +/- 0.20) - (14810 +/- 200)(T/K) from (945 to 1093) K; TmBr3(cr), log(p/kPa) = (11.67 +/- 0.20) - (14330 +/- 200)(T/K) from (921 to 1155) K; TmI3(cr), log(p/kPa) - (11.54 +/- 0.20) - (13790 +/- 200)(T/K) from (887 to 1051) K. Treating the results by second- and third-law methods, the standard sublimation enthalpies were determined to be Delta(sub)Hdegrees(298 K) = {(296 +/- 4) kJ.mol(-1) and (285 +/- 5) kJ.mol(-1)} for TmCl3 and TmBr3, respectively. For TmI3, the proposed enthalpy, Delta(sub)Hdegrees(298 K) = (277 +/- 4) kJ.mol(-1), was only derived by the second-law method. From this standard enthalpy, a set of free-energy functions and standard entropy, Sdegrees(298 K) = 227 J.K-1.mol(-1) for solid TmI3 was evaluated by third-law treatment of the data.