The new approach to structural reliability analysis based on order statistics and the expected time to first failure in a fleet of specified magnitude, that has been first proposed in a previous report AFML-TR-66-37 is developed in more detail and applied to structures subject to progressive fatigue damage. It is shown that the concept of fatigue sensitivity developed in WADD Tech. Rep. 61-53 is improved by relating it to the expected time to first failure rather than to the expected time to failure. The modified fatigue sensitivity factor becomes an effective parameter for the correlation of ultimate load and fatigue design and for the classification of fatigue sensitive structures.