Precise vapor-pressure data for solutions of lithium hydroxide in water from temperatures of 298.15-363.15 K have been measured by a procedure and equipment known to yield data of high precision. The investigated range of LiOH solution molality was from 0.07 to 4.77 mol.kg(-1). The values of the osmotic coefficient have been calculated, taking into account the second virial coefficient in the equation for the water vapor pressure. Adjustable parameters of Pitzer's model with Archer's extension and of the mean spherical approximation of a nonrandom two-liquid model were evaluated. The new experimental data are compared to literature values, which exhibit a surprising scattering.