A method of trimming blow-molded products while in the mold including the steps of placing a parison between a mold having two mold halves, moving the two mold halves together to form a cavity and enclose a portion of the parison, pressurizing the inside of the parison to produce a product and trimming a portion of the product while it is in the mold by applying a vacuum to those portions adjacent to a cutter and by then moving the cutter across the cavity and across the portion of the product to be cut. The mold halves are then separated and the product is removed therefrom. The apparatus for achieving this method includes a cutter slidably disposed in a first slot and having a slot plugging member slidably exposed in a second slot wherein the cutter and slot plugging member will prevent plastic from entering the first and second slots when the plastic product is being formed. After the plastic is formed, a vacuum is applied to portions of the product adjacent to the cutter. Then the cutter and slot plugging member can be actuated to cut through the product at the desired location.