Context: The need for the least ambiguous terminology for disorders affecting IGF-I production and action has become necessary with identification of defects at various steps in the GH-IGF-I axis and the promotion of new indications for and modalities of growth therapy. No generally agreed-upon or consensus-derived classification exists. Objective: Our objective was to designate all disorders affecting IGF-I production and action by their discrete location, as is already done with the defects in pituitary differentiation factors, avoiding imprecise and ambiguous terminology. Conclusions: We propose a pragmatic classification that is a precise listing of specific disorders sequentially following the GH-IGF-I axis, using their accepted designations, and the abolition of nonspecific or ambiguous terminology. This concept permits ready insertion of new discoveries.