The sublimation pressure of crystalline pentaerythritol tetranitrate has been determined over the temperature range (356 to 382) K by the torsion-effusion method. From simultaneous mass-loss determinations, the molecular weight of effusing vapor was found to be in accord with that of monomeric C(CH2ONO2)(4). Effusing vapor was also examined by mass spectrometry, extending the temperature-pressure range down to 302 K. The temperature dependence of pressure, determined by both torsion and mass-spectrometric methods, yielded enthalpies of sublimation in close agreement at (157.4 +/- 3.2) kJ(.)mol(-1). Earlier pressure measurements in the literature are lower by nearly a factor of 3, and the corresponding second-law sublimation enthalpy is also significantly lower.