Previously we proposed that the VACTERL association represents a dysmorphogenetic response of the primary developmental field, i.e., polytopic developmental field defects (DFD). As such, it should conform to the essential attributes of a DFD, namely, heterogeneity, homology, and phylogeneity. To study its heterogeneity, we analyzed the data of the Spanish Collaborative Study of Congenital Malformations (ECEMC). Our results confirm the observations indicating that the different patterns of defects that constitute this entity are not only clinically variable but also causally heterogeneous. This causal heterogeneity, which is of crucial importance in defining developmental fields, gives additional credence to the hypothesis that VACTERL constitutes a primary polytopic DFD.