A pipeline laid on an erodible sandy seabottom introduces a local disturbance in the wave/current flow that could cause the onset of scouring underneath the pipe itself. This could lead to a pipe self-lowering and/or to free spans formation and evolution. The investigation of the evolution of the pipe/seabottom configuration has significant relevancies for pipeline design as the action of waves and current might cause the vibration of unsupported sections of the pipeline and the accumulation of unacceptable fatigue damage. Therefore, a reliable design approach needs to estimate the evolutions of the pipe-seabed configuration in the first years after pipe laying, to identify the possible hazardous scenarios and to plan adequate corrective actions or pipeline inspection strategy. Numerous experimental investigations have been carried out to determine the critical conditions for onset of scouring and free-span development. These have led to the formulation of empirical relations between forcing agents (waves and current) and the relevant physical phenomena. Based on such formulas, a numerical model (PIPESOIL) for the time evolution of the pipe-soil configuration has been developed. In parallel, a numerical model (SPAFAT) for the fatigue analysis of free spans subjected to vortex induced vibrations and direct wave actions has been developed. The two models (PIPESOIL and SPAFAT) have been coupled in order to evaluate the fatigue damage that an evolving free span could accumulate under the same environmental conditions (waves and current) that are driving its evolution. Descriptions of the models, of their application and of typical results are presented in this paper. Copyright © 2007 by The International Society of Offshore and Polar Engineers(ISOPE).