In recent years,the state of deterioration of the bridges stock has been such that the volume of necessary works has reached un-manageable proportions in many countries.As budgets for maintenance,repair and rehabilitation are always limited and demands are constantly increasing,to find an optimal balance between cost and safety is today a new trend in bridge maintenance.Optimizing bridge maintenance and management is a strong expectation for owners and stakeholders facing aging bridge stocks and increasing aggressive traffic.In this context,the assessment of the structural performance may be necessary for various reasons thorough its lifetime.However,there are no standards or regulations on structural assessment in France compared to some countries.The studies upon a new Eurocode for the "Evaluation and rehabilitation of existing structures" are just starting and it will not be available before several years.For this reason,the French Ministry of Transport has decided to develop recommendations for the assessment of the structural performance of existing bridges.The paper summarizes todays practice and details the research work engaged in the calibration of appropriate partial factors for existing structures when investigation results are available.