The purpose was to develop two versions of a body function index in cerebral palsy (BFI-CP I and BFI-CP II) using two methods to explore the relationship and differences among them and the Gross Motor Function Classification System (GMFCS) and to explore the differences among subsets of the classifications that do not correspond to the ordinal levels of the GMFCS. Data on various measures from 405 children with CP between 18†months and 5†years of age were extracted from the Move & PLAY Study. The BFI-CP I was developed using a summing technique and the BFI-CP II was developed using cluster analysis. There was a strong correlation between the BFI-CP I and the GMFCS (r=0.92), between the BFI-CP II and the GMFCS (r=0.93), and between the BFI-CP I and II (r=0.92) all (p†<†0.001). There was also a significant difference between the BFI-CP I and the GMFCS (?2=670.49, df=16, p†<†0.001) and between the BFI-CP II and the GMFCS (?2=685.57, df=16, p†<†0.001). The findings of this study indicate that the two versions of the BFI-CP could be used as complementary methods in describing children with CP. © 2018 Taylor & Francis.