The present invention relates to antibodies and antigen-binding portions thereof that specifically bind to interleukin 5 (IL-5), which is preferably human IL-5. The invention also relates to human anti-IL-5 antibodies, including chimeric, bispecific, derivatized, single chain antibodies or portions of fusion proteins. The invention also relates to isolated heavy and light chain immunoglobulin molecules derived from anti-IL-5 antibodies and nucleic acid molecules encoding such molecules. The present invention also relates to methods of making anti-IL-5 antibodies, pharmaceutical compositions comprising these antibodies and methods of using the antibodies and compositions thereof for diagnosis and treatment. The invention also provides gene therapy methods using nucleic acid molecules encoding the heavy and/or light immunoglobulin molecules that comprise the human anti-IL-5 antibodies. The invention also relates to gene therapy methods and transgenic animals comprising nucleic acid molecules of the present invention.