This study confirms the clinical value of investigating the “iliacus complex” during evaluations of the low back. A new “iliacus test” isolates this iliacus complex component of limited hip extension. Designed for a single joint, the test isolates motion across the hip joint. Study results include the following: (1) in a comparison with the clinical standard, the Thomas test, data show that the two tests are significantly different in an asymptomatic population between the ages of 18 and 35 years; (2) with the exception of the standard Thomas test, the data show no statistical differences in range of motion when comparing the left side with the right side; (3) examiner-added, end-range pressure for assessment of range of motion when compared with the standard gravity-dependent end range of motion used in the Thomas test yields valuable new information; and (4) data provide a basis for population norms for each test–Thomas and iliacus–in gravity-dependent and examiner-produced tissue-feel end ranges.