The invention relates to a method for recovering energy from the organic fraction of urban solid waste comprising the following steps: a) the organic fraction is pre treated with mineral acids, preferably sulfuric acid, during which the fraction is heated by an outer thermal jacket with no steam injection or steam explosion, thereby producing a first slurry containing an insoluble solid susceptible to enzymatic attack by cellulases; b) a step comprising enzymatic hydrolysis using cellulases and simultaneous fermentation, using an ethanologenic microorganism, of the first slurry in order to obtain a second slurry containing diluted ethanol; and c) distillation of the second slurry such as to obtain wet ethanol, a recyclable liquid effluent and a solid.