Monoclonal antibody G250 (mAbG250) recognizes a determinant on carbonic anhydrase IX (CAIX). CAIX is expressed by virtually all renal cell carcinomas of the clear cell type (ccRCC), but expression in normal tissues is restricted. The homogeneous CAIX expression in ccRCC and excellent targeting capability of mAbG250 in animal models led to the initiation of the clinical evaluation of mAbG250 in (metastatic) RCC (mRCC) patients. Clinical studies confirmed the outstanding targeting ability of mAbG250 and cG250 PET imaging, as diagnostic modality holds great promise for the future, both in detecting localized and advanced disease. Confirmation of the results obtained in the non-randomized clinical trials with unmodified cG250 is needed to substantiate the value of cG250 treatment in mRCC. cG250-Based radio immuno-therapy (RIT) holds promise for treatment of patients with small-volume disease, and adjuvant treatment with unmodified cG250 may be of value in selected cases. In the upcoming years, ongoing clinical trials should provide evidence for these assumptions. Lastly, whether cG250-based RIT can be combined with tyrosine kinase inhibitors, which constitutes the current standard treatment for mRCC, needs to be established.