The present study deals with the synthesis and characterization of cross-linked chitosan microspheres containing an hydrophilic drug, hydroquinone. The microspheres were prepared by the suspension cross-linking method using glutaraldehyde as the cross-linking agent of the polymer matrix. Perfectly spherical cross-linked hydrogel microspheres loaded with hydroquinone were obtained in the size range of 20-100 mum. The effect of the degree of polymer cross-linking, chitosan molecular weight, chitosan concentration and amount of the encapsulated drug on the hydroquinone release kinetics was extensively investigated. It was found that slower drug release rates were obtained from microspheres prepared by using a higher initial concentration of chitosan, a higher molecular weight of chitosan or/and a lower drug concentration. Most importantly, it was shown that the release rate of hydroquinone was mainly controlled by the polymer cross-linking density and, thus, by the degree of swelling of the hydrogel matrix.