Occupational doses received during the operation and maintenance of Ontario Hydro’s pressurized heavy water nuclear power reactors are reported and comparisons made with occupational doses received during the operation of other reactor types in various nuclear power programs. The organizational and technical factors that have contributed to significant occupational dose reductions in Ontario Hydro’s program over the past 20 yr are discussed. Dose reduction practices in the design and operation of Ontario Hydro’s nuclear power reactors are described.