The goals of the present investigation were to identify the prevalence of acetabular dome retroversion in a mixed race population, to quantify the average amount of cross-over ratio, and to determine normative values. The presence of the cross-over sign and its overlap ratio was assessed for 2,925 hips meeting strict radiographic criteria of the pelvic radiograph. Fifty-two percent of the hips had no cross-over sign whereas 48% had at least a minimal amount of overlap of the anterior and posterior acetabular wall. Analysis of only those hips with positive cross-over sign revealed a mean cross-over ratio of 26% +/- 11% (range: 3 to 93). Forty-two percent of the patients had no cross-over on either side, 18% on one side, and 40% on both sides. The presence of the cross-over sign is more common than previously expected. Further studies will be necessary to determine the risk of pathological abnormality and to correlate symptoms to crossover ratios. Surgery should not be based solely on the finding of a cross-over sign without clinical correlation.