A search for invisibly decaying Higgs bosons is performed using data taken with the OPAL detector at LEP at centre of mass energies between 183 and 209 GeV, corresponding to a total integrated luminosity of approximately 660 pb-1. No excess of events over the expected background from Standard Model processes is observed. Limits on the production of invisibly decaying Higgs bosons produced in association with a Z0 boson are derived at the 95% confidence level. Assuming a branching ratio BR(h0 -> invisible) = 1, a lower limit on the Higgs boson mass is also placed.