The reactions following 257 nm photolysis of CH3I multilayers on TiO2(110) at 90 K were investigated using quadrupole mass spectrometry. The observed photofragments that desorb from the surface are CH4, C2H6, I-2, CH2I2, and C2H5I. The linear dependence of the methane and ethane on laser fluence and the absence of a kinetic isotope effect in the formation of methane are consistant with the reaction mechanism in which the hot methyl photofragments react with parent molecules. The relative ratios of photoproducts are different from those observed in the photolysis of gas, liquid, and solid phases and from those observed for CH,I multilayers on a metallic surface at lower fluence.