Slurry bubble column photocatalytic reactors have been used for photocatalytic wastewater treatment. In order to design and optimize these reactors, the light distribution needs to be determined. In this work, the light distribution in a slurry bubble column photocatalytic reactor was simulated using the Monte Carlo model. The model was validated using total transmitted radiation (TTR) measurements. The validated model was then used to determine the local volumetric rate of energy absorption (LVREA) and volumetric rate of energy (VREA) profiles. Very good agreement was achieved between experimental and simulated TTR values at different catalyst loadings using a Henyey-Greenstein scattering parameter of 0.84. The Monte Carlo model was more accurate than the six-flux model. From an analysis of the LVREA profiles, the light distribution along the radial coordinate was found to be highly non-uniform. Using the VREA, the optimum catalyst loading was estimated to be 0.4 g/L. Bubbles were observed to slightly decrease the TTR while slightly increasing the light absorption especially at low catalyst loadings; therefore, bubble simulation could be neglected without significant loss of accuracy. This work highlights the accuracy and utility of Monte Carlo simulation for determining the light distribution in an annular slurry bubble column photocatalytic reactor. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.