The X-ray structures of the title compounds have been determined from diffractometer data by the heavy-atom method and refined by least-squares. Crystal data: [Cu(C₃H₆N₂S)₄]NO₃, (I), a= 13.22(1), b= 11.21(1), c= 7.55(1)Å, α= 82.0(1), β= 78.3(1), γ= 87.2(1)°, Z= 2, space group P, final R 8.5%; [Cu(C₃H₆N₂S)₂Cl]₂, (II)a= 7.43(1), b= 18.71(1), c= 16.37(1)Å, β= 94.4(1)°, Z= 4, space group P2₁/c, final R 9.4%. In (I) copper co-ordination is tetrhedral and involves the sulphur atoms of four 2-thioimidazolidine (etu) molecules (Cu–S 2.34, 2.36, 2.34, and 2.33 Å). Complex (II) is binuclear containing two kinds of Cu^I atoms: one tetrahedrally co-ordinated by three etu molecules (Cu–S 2.26, 2.28, and 2.63 Å) and by one chlorine ion (Cu–Cl 2.32 Å), the other trigonally co-ordinated by two etu molecules (Cu–S 2.20 Å) and one chlorine ion (Cu–Cl 2.28 Å). In both compounds conformation and packing are mainly determined by hydrogen bonds of the type N–H ⋯ O (I) or N–H ⋯ Cl (II), and N–H ⋯ S.