The management of a Life Insurance Company or a Pension Fund must take into account the temporal evolution of its assets and its liabilities. The variables we work here are the factors and returns representing assets and liabilities; as illustration purpose, numerical data have been taken from the Spanish Market. The past performance of these variables is analysed statistically and we deduce a Vector Error Correction Model (VECM) to model their behaviour. In the process of scenario generation we simulate different trajectories for each of the variables (return or factor) with a probability of occurrence associated to each trajectory. Risk is related to adverse results and to a first approximation is measured by the Value at Risk over a give...