Fatigue and corrosion fatigue are responsible for the majority of drillstring failures. The complexity of fatigue and the inability of the drillstring designer to account for a great many factors affecting fatigue make it impractical or impossible to predict accurately the fatigue life of a drillstring component. The full-length paper describes a comparative design approach that normalizes many factors affecting fatigue that generally are unknown to the designer, permitting the fatigue performance of available alternatives to be compared quantitatively on the basis of what is known. The method has proved effective in field use.