The GMFM is a validated evaluative instrument designed to detect change in gross motor function of children with cerebral palsy. Intraclass correlation coefficients (ICCs), calculated to study interobserver and intraobserver reliability, were high. In our study, we used a Dutch translation of the GMFM. Interobserver reliability and test-retest reliabilty of the Dutch version of the GMFM were assessed in a sample of children with mild, moderate, or severe cerebral palsy. The ICC for inter- observer reliability for the first dimension (lying and rolling) was .75; ICCs for the other dimensions ranged from .96 to 1.00. The ICCs for test-retest reliability ranged from .96 to .99 for the 5 dimensions. The evaluative quality of the GMFM has been confirmed in a study in which the Dutch version was used.