The effect of a hydrophilic polymer, hydroxypropylmethyl cellulose K4M, on the complexation of diclofenac sodium with b- and hydroxypropyl-b-cyclodextrins has been studied. Multicomponent systems were prepared with the drug, both cyclodextrin and the polymer. Phase solubility diagrams revealed the positive effect of the polymer on the complexation of the drug but this effect was found after autoclaving the solutions. Solid inclusion complexes were prepared by freeze-drying and characterized by thermal analysis (DSC) and X-ray diffractometry. In solid state, binary inclusion complexes enhance the dissolution behaviour of diclofenac but, from the b-cyclodextrin multicomponent complex, the polymer controls the release of the drug. In the case of hydroxy- propyl-b-cyclodextrin multicomponent system, the solubility of the drugs increases significantly compared with the binary complex.