Objective: The amount of residual monomer is one of the principal factors affecting the properties of acrylic resin denture bases. In recent years, glass fibers have been used to strengthen denture base resins. The purpose of this study was to investigate the effect of glass fiber reinforcement on the amount of residual methyl methacrylate released from two different denture base resins (heat cured and autopolymerized). Method and materials: Continuous unidirectional and woven preimpregnated glass fiber reinforcements (Stick and Stick Net) were used to reinforce heat-curing and autopolymerizing denture base resins. Results: The release of residual methyl methacrylate from heat-cured and autopolymerized test specimens reinforced with glass fibers was significantly higher than that from unreinforced test specimens. Stick Net glass fiber reinforcement resulted in significantly higher residual monomer release than did Stick glass fiber reinforcement. Test specimens made from heat-cured denture polymethyl methacrylate released less residual methyl methacrylate than did specimens made from autopolymerized polymethyl methacrylate. Conclusion: Glass fiber reinforcement increases the residual monomer content of denture base resins. The level of residual monomer ranged from 0.11% to 0.37% in heat-cured resin and from 0.18% to 0.46% in autopolymerized denture base resin.