A kinetic model is developed to simulate the biodegradation of the organic fraction of municipal solid waste in a high-solids complete-mix continuous-flow anaerobic digestion process. A mass balance correction factor (f) is used to account for (i) the water that is incorporated into the production of biogas, and (ii) the water vapor present in the biogas. With the inclusion of the factor f, expressions are developed to determine the substrate removal efficiency based on first-order and Monod kinetic models. Simulations using first-order and Monod kinetic models are carried out to illustrate the importance of the f factor on the substrate mass removal and microorganism concentration in the high-solids anaerobic digestion process. The effect of the value off on kinetic constants, and the error involved in considering the high-solids process as a low-solids process are discussed. Finally, experimental results from a pilot-scale high-solids complete-mix batch-fed anaerobic digestion process are used to estimate the first-order rate constant for the biodegradable fraction of municipal solid waste.