The regio- and stereoselectivity in the solvomercuriation and intramolecular alkoxymercuriation of several cyclic olefinic alcohols were examined. The regioselectivity is controlled mainly by electronic factors, while the stereoselectivity is controlled by steric factors as well as electronic ones. The optimised structure of the mercurinium ion intermediate suggests that the attractive interaction between the hydroxy group in the molecule and the mercurinium ion moiety affects the selectivity.