Background The Trunk Assessment Scale for Spinal Cord Injury (TASS) and the Trunk Control Test for individuals with a Spinal Cord Injury (TCT-SCI) are highly reliable assessment tools for evaluating the trunk function of individuals with SCIs. However, the potential differences in the validity of these two scales are unclear. Objectives To evaluate the criterion validity of the TASS and the construct validity of the TASS and TCT-SCI. Participants and Methods We evaluated 30 individuals with SCIs (age 63.8 ± 10.7 yrs, 17 with tetraplegia). To evaluate criterion validity, we calculated Spearman's rho between the TASS and the gold standard (the TCT-SCI). To determine construct validity, we used the following hypothesis testing approaches: (i) calculating Spearman's rho between each scale and the upper and lower extremity motor scores (UEMS, LEMS), the Walking Index for SCI-II (WISCI-II), and the motor score of the Functional Independence Measure (mFIM); and (ii) determining the cut-off point for identifying ambulators with SCIs (≥ 3 points on item 12 of Spinal Cord Independent Measure III) by a receiver operating characteristics analysis. Results A moderate correlation was confirmed between the TASS and the TCT-SCI (r = 0.68). Construct validity was supported by six of the eight prior hypotheses. The cut-off points for identifying ambulators with SCIs were 26 points (TASS) and 18 points (TCT-SCI). Conclusion Our results indicate that the contents of the TASS and the TCT-SCI might reflect the epidemiological characteristics of the populations in which they were developed.