The aim of the study was to monitor the changes over an eight-month period in gross motor performance of a group of children with different types of cerebral palsy (CP) using the GMFM (Gross Motor Function Measure). Fifty children aged between 12 and 79 months and undergoing active physical therapy (twice a week) participated in the study. The children were evaluated three times at four-month intervals (baseline, four, and 8 months later) with the GMFM test under standardized conditions. Children with quadriplegia (n = 24), hemiplegia (n = 16), and diplegia (n = 10) showed significant improvement of their gross motor function over the eight-month period (mean GMFM total change score = 6.2%; 4.2%, and 7.0%, respectively) and there was no difference in the rate of change across types. The mean GMFM scores of the children with quadriplegia were always significantly lower than corresponding scores of the two other groups (p < 0.001). Results indicate that, irrespective of the type of CP, the GMFM is sensitive to changes in motor performance of children over time.