Ab initio calculations, using a slightly modified version of the second-order Gaussian-2 procedure, have been performed to determine the thermochemistry of disulfur decafluoride, S2F10. The results include Delta(f)H(0) degrees(S2F10)=-1880 kJ/mol and Delta(f)H(298)degrees(S2F10)=-1903 kJ/mol, with an estimated uncertainty of 8 kJ/mol (2 sigma). This implies sulfur-sulfur bond strengths D-0 degrees(F5S-SF5)=195+/-8 kJ/mol and D(298)degrees(F5S-SF5)=198+/-8 kJ/mol. For comparison, second-order Gaussian-2 calculations of S-2 and S-8 yield S-S bond energies in error by only -6 kJ/mol and +3 kJ/mol, respectively. The torsional barrier in S2F10 is calculated to be 40+/-5 kJ/mol, indicating that torsional motion is negligible at 298 K. Minor reassignments are made in the experimental vibrational spectrum. Some comparisons between conventional and density-functional calculations are also made.