Single crystal X-ray structures of solvated forms of theanthelmintic drug Niclosamide reveal distinctly differentmodes of inclusion for different solvents. These modes are,respectively, cavity occupation by water molecules in 1 : 1niclosamide.H₂O, channel occupation by tetrahydrofuranmolecules in 1 : 1 niclosamide.THF, and intercalation bytetraethylene glycol molecules in 2 : 1 niclosamide.TEG. Inall three compounds the host drug molecule adopts the same,nearly planar conformation, which is maintained by anintramolecular N-H.O hydrogen bond. Host-guest recognitioninvariably involves hydrogen bonding between the drughydroxyl group and an oxygen acceptor atom of the solventmolecule. The observed modes of solvent inclusion can bereconciled with the behaviour of the crystals on heating.