The stereoselective hydrogenation of dibenzo-18-crown-6 ether in the cis-syn-cis isomer of dicyclohexano-18-crown-6 ether has been investigated using either supported metal catalysts or colloidal metal particles prepared under phase transfer catalysis conditions. Supported catalysts generally lead to a mixture of isomers with a poor stereoselectivity in cis-syn-cis. In contrast, when phase transfer agents like tertiary amines and ammonium salts were used in a biphasic system, a good selectivity was achieved under mild conditions. The effect of different factors such as the nature and concentration of the phase transfer agents upon the selectivity has been investigated. An increase of the hydrogen pressure to 5 MPa leads to a cis-syn-cis/cis-anti-cis isomer ratio of 95/5. Strong evidence for the heterogeneous nature of the catalysis involved is presented. A mechanism involving the phase transfer agent as a modifier on the surface of the colloidal rhodium particles is proposed.