A number of slopes that have been stable during many years may fail when an extraordinary rain period occurs. This phenomenon involves not only the lithology, the geometric and the mechanical characteristics of the slope but also the rain-evaporation-infi ltration regime of the site. In this paper, the stability of a slope in the comunity of San Juan de Grijalva, Ostuacán, Chiapas (Mexico) that failed during an intense raining period is analyzed. The volume of this slide was over 5 millions of cubics meters of soil and it produced the obstruction of the Grijalva river. The stratigraphic and geometric properties of the slope were determined and undisturbed samples were obtained in the site to determine the mechanical properties of the material. The stability analysis considered the variation of the cohesion of the soil caused by we ing and it was possible to observe the evolution of the safety factor with the water content of the material. Through the analysis of the rain infi ltration and the stability of the slope, it has been possible to reproduce the failure process.