Dichloro-(1,3,5-trithian)mercury(II) crystallises in the orthorhombic system, space group Pbcm, with four molecules of C3H6Cl2HgS3 in a cell of dimensions a= 4·29, b= 14·33, c= 13·62 Å. The mercury atom is co-ordinated in a distorted tetrahedral manner by two sulphur atoms at 2·61 Å and two chlorine atoms at 2·44 Å. The angles SHgS and ClHgCl are 113 and 117°, respectively. The trithian molecule is in the chair conformation and the S–Hg bonds are equatorial.