An anatomic basis for carpal tunnel syndrome (CTS) has been proposed but not confirmed; both volumetric and area studies have been used to address this issue. The authors have demonstrated that the ratio of the carpal tunnel contents (CTC) to carpal tunnel volume (CTV) provides information regarding the relative free space in the carpal tunnel as compared with canal volume alone. This study was undertaken to determine whether the CTC/CTV ratio was higher for patients with CTS than for normal subjects. Seven asymptomatic volunteers and 7 patients with symptoms of CTS underwent magnetic resonance imaging (MRI) so that the CTC/CTV ratios could be determined. Standard radiographs were analyzed to identify plain radiographic variables that differed between patients with CTS and control subjects, and no differences were found. On MRIs, however, CTC/CTV ratios were noted to be higher for patients with CTS than for matched control subjects.