The anaerobic digestion model No. 1 (ADM1), conceived by the international water association (1WA) task group for mathematical modelling of anaerobic digestion processes is a structured generic model which includes multiples steps describing biochemical and physicochernical processes encountered in the anaerobic degradation of complex organic substrates and a common platform for further model enhancement and validation of dynamic simulations for a variety of anaerobic processes. In this study the ADM I model was modified and applied to simulate the mesophilic anaerobic co-digestion of olive mill wastewater (OMW) with olive mill solid waste (OMSW). Tile ADM I equations were coded and implemented using the simulation software package MATLAB/Sirnulink. The most sensitive parameters were calibrated and validated using updated experimental data of our previous work. The results indicated that the ADM I model could simulate with good accuracy: gas flows, methane and carbon-dioxide contents, pH and total volatile fatty acids (TVFA) concerttrations of effluents for various feed concentrations digested at different hydraulic retention times (HRTs) and especially at HRTs of 36 and 24 days. Furthermore, effluent alkalinity and ammonium nitrogen were successfully predicted by the model at HRTs of 12 and 24 days for some feed concentrations. (c) 2007 Elsevier Ltd. All rights reserved.