Use of a shank shell has been shown to estimate tibial transverse rotations better than skin-mounted markers. However, the day-to-day reliability of the transverse tibial rotations using an individually molded shank shell has not been previously investigated. This study examined the between-tests and trials reliability of an individually molded shank shell for measuring peak tibial internal and external rotations, time of peak values, and tibia range of motion during 5 walking trials. The trial-to-trial reliability of tibial transverse rotations was measured in 14 healthy individuals while the test-retest reliability was measured in 10 persons on two occasions. Trial-to-trial reliability for peak transverse rotations, time of peak values, and tibia range of motion ranged from ICC (3,1) 0.59–0.95. The PCA between trials showed that 88–99% of values were within 3° of agreement. Test-retest reliability for peak rotations, tibia range of motion, and time of peak values ranged from ICC (3,1) 0.70–0.89 with
SEM1.6–2.21°, 0.021%, and 0.034%, respectively. The PCA between tests showed that 70–100% of values were within 3° of agreement. The use of an individually molded shell and the close attachment of the shank shell to the individual's shank resulted in reliable test-retest and trial-to-trial data.