This study evaluated the influence of specimen dimensions and storage medium and temperature on the flexural properties of one dental resin composite. The material utilized throughout the study was Clearfil AP-X. Eighty specimens were built with dimensions of either 10×2×2 mm or 25×2×2 mm, stored dry or in distilled water, at 25 or 37ºC, for 24 h. Flexural strength and modulus were tested in three-point bending. Results were evaluated with three-way ANOVA and Tukey's test (α=0.05). Statistical significance was observed for all three factors: temperature (37ºC=190.8 MPa, 25ºC=165.3 MPa; p<0.01), storage medium (water=167.7 MPa, Dry=188.4 MPa; p<0.01) and specimen dimensions (10×2×2 mm=197.9 MPa, 25×2×2 mm=158.2 MPa; p<0.01). None of the interactions were significant. Within the limitations of this study, it can be concluded that factors such as specimen dimensions, storage medium and temperature significantly affect flexural strength results, which invalidates comparisons of results from studies that use different methodologies.