The interaction of ThCl₄·nH₂O with 1,4,7,10,13,16-hexaoxacyclo-octadecane (18-crown-6) in ethanol yields crystalline [ThCl₄(OHEt)₃(OH₂)]·(18-crown-6)·H₂O. The crystal structure of this complex has been determined from three-dimensional X-ray diffraction data collected by counter methods. It crystallizes in the triclinic space group P, with (at –150 °C)a= 10.486(3), b= 10.859(5), c= 16.092(6)Å, α= 75.45(4), β= 72.41(4), γ= 60.58(4)°, and D_c= 1.79 g cm^–3 for Z= 2. The final R value was 0.059 for 4 759 independent observed [F_o 5σ(F_o)] reflections. The thorium atom is eitht-co-ordinate with square antiprismatic geometry. The four chlorines occupy trans positions in opposite square planes, with co-ordination completed by one water molecule and three ethanol groups. Two ethanolic hydrogen atoms participate in inter- and intra-molecular bifurcated hydrogen bonds to two of the chlorine atoms. The co-ordinated water molecule is hydrogen-bonded to the crown ether and the second water molecule. The third ethanol group is hydrogen-bonded to the other side of a symmetry related crown ether. The resulting ‘supermolecule’ consists of infinite zigzag chains (crown–metal–crown–metal) with the chains linked via the intermolecular ethanolic hydrogen to chlorine hydrogen bonds. The crown ether has the symmetric D_3d conformation. The Th–Cl separations average 2.790(4)Å(hydrogen-bonded chlorines) and 2.694(3)Å.