AgScP2Se6, AgErP2Se6 and AgTmP2Se6 were obtained by high temperature reaction of stoichiometric amounts of the elements in evacuated silica ampoules. They crystallize in the space, group P (3) over bar 1c, Z = 2 with the lattice constants a = 6.463(1) angstrom c = 13.349(1) angstrom (AgSeP2Se6), a = 6.578(1) angstrom, c = 13.410(2) angstrom (AgErP2Se6), and a = 6.567(1) angstrom, c = 13.422(1) angstrom (AgTmP2Se6). The crystal structures of AgScP2Se6 and AgErP2Se6. were relined from merohedrally twinned crystals. No twinning was observed for AgTmP2Se6. The crystal structures are isotypic and call be described as a variant of the Cdl(2) structure type. Thus, selenium atoms, are hexagonally close packed. The octahedral voids of every second layer are occupied by Ag, M3+ (M = Sc, Er, Tm), and P-2 dumbbells in an ordered fashion. The crystal structures are isotypic to AgScP2S6 and AgInP2S6.