Standardized scales to evaluate qualities of trunk movements in children with dysfunction are sparse. An examination of the reliability of scales that may be useful in the clinic is important. The aim of this study was to examine the reliability of the Trunk Impairment Scale (TIS) for children with cerebral palsy (CP). Standardized scales are useful for treatment planning and evaluation. This was an intra- and inter-observer reliability study. Video recordings of 25 children, 20 with CP and 5 with no motor impairment, in the age group 5-12 years of age, were analyzed by three observers on two occasions. Intraclass correlation coefficients (ICC [1,1] and [3,1]) with 95% confidence intervals, standard error of measurement, kappa values and percent agreement, and Bland-Altman Plots were calculated. The relative reliability (intra- and inter-observer reliability) was very high for the total score and subscale score of the TIS: ICC [1,1] and [3,1] varied between 0.94 and 1.00. Kappa values for the items ranged from 0.45 to 1.00. The absolute reliability values for the parameters are reported. The Bland-Altman analysis showed consistency of scores. This study indicates that TIS is a reliable measure of trunk control for children, 5-12 years of age, with CP. (Contains 5 tables and 1 figure.)