The effects of age, gender, and laterality on sacroiliac/sacral ratios obtained during quantitative joint imaging were assessed in 97 nonarthritic control subjects. For the entire group, the right sacroiliac-to-sacral mean ratio of 1.27 in 54 males was significantly higher (p less than 0.02) than the right mean ratio of 1.18 in 53 females. In both genders the right joint ratio tended to be higher than the left in all age groups. The difference in mean ratio between the two joints was wider for males than for females. The age did not affect the joint ratio in either gender. It is concluded that the range of normal sacroiliac-to-sacral ratios are different for males and females and should be taken into account during a quantitative sacroiliac joint imaging examination.