The standard molar enthalpy of formation of monoclinic 2-hydroxybenzoic acid (2-OHBA), at T = 298.15 K, was determined as Delta(f)H(m)(0) (2-OHBA, cr, monoclinic) = - (591.7 +/- 1.3) kJ (.) mol(-1), by combustion calorimetry. The static-bomb calorimeter used in this work and the accuracy tests performed with nicotinic acid are also described.