Front tile j,iitc)rsiti' ()/OticJtt'a (111(1 Ottatta Genera! Hospital We describe a new method for the accurate measurement of the angle of anteversion of an acetabular cup from standard anteroposterior radiographs, and provide the conversion tables required. The effect of the centring of the radiograph is discussed and a method of distinguishing between anteversion and retroversion by using a caudally directed x-ray beam is described. Dislocation is an ominous complication of total hip replacement: its reported incidence ranges from 0.6% (Etienne, Cupic and Chamnley 1978) to 7.0%