Polycrystalline samples with nominal formula CeM 2B 2C (M=Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Pt and Au) were prepared by arc melting. CeM 2B 2C essentially forms as a single phase with the LuNi 2B 2C-type structure only for M=Co, Ni, Rh, Pd, Ir and Pt. CeOs 2B 2C exists as a minority phase in the corresponding alloy. No CeM 2B 2C phase could be detected in the alloys melted with M=Fe, Cu, Ru, and Au. Highly accurate structural parameters were obtained by single crystal diffractometry on CeRh 2B 2C and CeIr 2B 2C. None of these compounds exhibits superconductivity or magnetic order down to 2 K. From X-ray absorption spectroscopy (XAS) measurements, we conclude that the Ce ions have a non-integer valence in CeM 2B 2C (M=Co, Ni, Rh, Ir), but are nearly trivalent in CePd 2B 2C (in contrast to an earlier report) and in CePt 2B 2C. The magnetic and valence properties of the CeM 2B 2C series show a regular evolution from delocalised to localised 4f-electron states driven by the value of the atomic radius of the M metal. For all these compounds, the Ce–Ce distances (‘ a’ parameter) are larger than the Hill limit (≈3.4 Å), clearly suggesting the importance of 4f– nd overlaps.