Reported are the synthesis and structure of the anionic intermetalloid cluster [Bi12Ni7(CO)(4)](4-). It was synthesized from the known smaller clusters Bi3Ni4(CO)(6)(3-), Bi3Ni6(CO)(9)(3-), and Ni@Bi6Ni6(CO)(8)(4-) by their aggregation as a result of thermal deligation and oxidation. The new cluster is structurally characterized by single-crystal X-ray diffraction in the compound (K[crypt])(4)[Bi12Ni7(CO)(4)] (1), and its presence in solution is confirmed by electrospray mass spectrometry. It can be viewed as composed of a Ni-centered icosahedral core of Bi6Ni6(CO)(4) where two diametrically opposed Ni atoms are capped by Bi-3 triangles. However, its electron count is rationalized based on a structure made of fused tetrahedra.