The present disclosure relates to anti-ROR1 binding proteins, including those that bind to a ROR1 or portion thereof such as an intracellular C terminal portion of a ROR1 protein, and the use of such binding proteins in immunohistochemical and diagnostic methods. Related kits and methods of using the binding proteins are also provided, as are methods of treatment of subjects having diseases or conditions determined to be candidates for such treatments by the binding proteins or methods of this disclosure.