Through this article, the degree of polymerization attainable in a commercial acrylic bone cement based on poly(methyl methacrylate) (PMMA) was investigated by differential scanning calorimetry (DSC) and gas chromatography( GC). The results obtained revealed a marked dependence between the maximum monomer conversion and the cure temperature. Specimens for the mechanical evaluation of the cement were subjected to two different cure conditions : one set of samples was allowed to cure at room temperature and an additional set was also postcured at 140 degrees C for 2 h. The latter thermal treatment permitted one to discard the presence of the unreacted monomer in the hardened material. The effect of the unreacted monomer on the mechanical behavior was evaluated by measuring the flexural modulus (E), the compressive yield stress (a,), and the fracture toughness (K-IC). Samples prepared at room temperature for mechanical evaluation contained residual monomer which acts as a plasticizer of the matrix, increasing K-IC and decreasing E and a,. The cure temperature and mold dimensions influence the amount of the residual monomer in the hardened material. Thus, differences in the values of the mechanical properties measured for the same commercial formulation may be attributed to a different mold dimension used in the test.