Isothermal desorption experiments to study the kinetics of the desorption of hydrogen from the diamond (100)2x1 surface are described. The surface hydrogen concentrations are measured using direct recoil spectroscopy, an ion spectroscopy in which ions and neutral species recoiled from the surface are detected by time-of-flight measurements. Results indicate that the desorption of hydrogen from diamond (100) is zeroth order at temperatures below 800 degrees C and changes to first order above 825 degrees C. In the first-order region, the measured activation barrier is 39 kcal/mol and the pre-exponential factor is 3.2x10(5) s(-1).