The present invention relates to mammalian antibodies, designated 12B1 and antigen-binding portions thereof that specifically bind to insulin-like growth factor I receptor (IGF-IR), preferably human IGF-IR. Also included are chimeric, bispecific, derivatized, single chain antibodies derived from the antibodies disclosed herein. Nucleic acid molecules encoding the mammalian antibodies as well as methods of use thereof are also disclosed. Also included are pharmaceutical compositions comprising these antibodies and methods of using the antibodies and compositions thereof for treatment and diagnosis of pathological hyperproliferative oncogenic disorders associated with expression of IGF-1R.