Resistance to passive movement in children with spastic cerebral palsy was assessed by two raters using the Modified Ashworth Scale and the Modified Tardieu Scale. Four muscle groups in the lower limbs were tested using a standardized procedure. Interrater reliability of the scales was evaluated by the intraclass correlation coefficient. Seventeen children, with a mean age of 7 years 9 months, were included. Two children were rated twice. The intraclass correlation coefficients of both scales were low and did not reach the acceptable limit of 0.75. Caution should be used when these scales are applied.