Y₃Co₂ crystallizes with a new orthorhombic structure type. Space group Pnnm (No. 58); a= 12.248, b=9.389, c=3.975 Å; Z=4, Dx=5.58 g cm⁻³, F.W. 384.58, F(000)=684, μ(Mo Kα=426 cm⁻¹, R = 0.10. The structures of Y₃Co₂ and the earlier determined Dy₃Ni₂ are shift structure variants. Both structures are characterized by infinite bands formed by joining four infinite trigonal prism columns. The arrangement of these bands is, however, different in the two structure types. Slicing one of the structure types in blocks of equal size and shifting them with respect to one another leads to an atom arrangement characteristic of the other structure type.