In this paper, the critical and the optimum conditions for thermophilic-dry anaerobic digestion have been determined employing two types of Organic Fraction of Municipal Solid Waste (OFMSW): synthetic (average particle size of 1 mm) and industrial (average particle size of 30 mm). On the basis of the methane production rate and the removal percentage of organic matter achieved, four SRT were tested to determine the values of the critical and optimum parameters for each waste. The results point to a SRT of 15 days as the optimum SRT for both types of waste. In the case of the synthetic OFMSW, this SRT is characterized by an organic loading rate of 11.8 x 10(3) mg VS/Ld. To the industrial OFMSW, the organic loading rate corresponding to this SRT is 2.93 x 10(3) mg VS/Ld. On the other hand, the SRT from which takes placed a destabilization of the process depends on the type of waste. For the synthetic OFMSW, this SRI was 8 days (22.1 x 10(3) mgVS/Ld), whereas for the industrial OFMSW it was 10 days (4.39 x 10(3) mgVS/Ld). (C) 2011 Elsevier B.V. All rights reserved.