The crystal structure of indium(rr1) dithizonate, [In( Hdz)J, has been determined by single-crystal X-ray diffraction methods at 295(1) K, and refined by least squares to a conventional residual of 0.043 for 3 081 ' observed ' reflections. Crystals are triclinic, space group P7, with a = 18.469( 6), b = 14.928(7), c = 7.570(4) A, a = 80.31 (4), f3 = 86.58(4), y = 75.48(4)", and Z = 2. The asymmetric unit of the structure is the mononuclear [In( Hdz),] molecule ; the indium atom is trigonally bipyramidal, five co-ordinated, one ligand being unidentate and co-ordinated equatorially through the sulphur [In-S 2.468(3) A], while the other two are bidentate (N,S), spanning axial and equatorial positions. The axial In-N distances are 2.372(6) and 2.334(6) A, while the associated equatorial In-S distances are 2.477(3) and 2.467(3) A.