The SX diatomics, X = first- or second-row atom, have been studied employing coupled cluster theory and the aug-cc-pV(X+d)Z basis sets. To estimate ΔfH°298, we have included a correction for core−valence (CV) correlation, spin−orbit splitting, and scalar-relativistic (SR) effects. For SO and SC, the estimated ΔfH°298 values are 0.5 kcal/mol within the experiment. However, for the remaining molecules, a revision of their ΔH°f,298 are required. Deviations as large as 10 kcal/mol have been found between our best estimates and the values adopted by the NIST-JANAF tables. The proposed ΔfH°298 (±0.5kcal/mol) are 67.6 (SB), 66.7 (SN), 0.8 (SF), 47.4 (SAl), 27.9 (SSi), 38.1 (SP), 29.4 (S2), and 27.1 (SCl) kcal/mol. For comparative purposes we performed BD(T), G3, CBS-QB3, B3LYP, and B3PW91 calculations. The mean absolute error (MAE) of the G3 and CBS-QB3 ΔfH°298 with respect to our best results is 1.0 kcal/mol for both methodologies, whereas for B3LYP/6-311+G(3df) and B3PW91/6-311+G(3df), the MAE is 1.6 and 2.0 k...