The rare earth-rich intermetallic compounds RE4OsCd (Gd4RhIn type, RE = La–Nd, Sm, Gd) and RE10OsCd3 (Er10FeCd3 type, RE = Y, Sm, Gd–Tm, Lu) were synthesized by induction melting of the pure elements in sealed niobium ampoules and characterized through their X-ray powder patterns. The structures of Ce4OsCd, Nd4Os0.83Cd1.17, Sm9.87OsCd3.13, and Tm9.89OsCd3.11 were refined from X-ray single crystal diffractometer data. These intermetallics are the first ternary osmium–cadmium compounds. The striking structural feature is an adamantane-like network of osmium-centered trigonal prisms in the RE4OsCd phases with Cd4 tetrahedra (308 pm Cd–Cd in Ce4OsCd) in the cavities. The RE10OsCd3 phases exhibit triangular Cd3 clusters (328 pm Cd–Cd in Sm9.87OsCd3.13) which, together with rare earth atoms, form chains of corner- and face-sharing Cd3RE tetrahedra. Further motifs are Os@RE6 trigonal prisms (TP) that are condensed to empty RE6 octahedra (O), building infinite…TP–O–O… rows in c direction. The two types of rows show the motif of a hexagonal rod packing.