Purpose: The aim of this study was to evaluate the diffusion of 2-Hydroxyethyl methacrylate (HEMA) from resin cement through dentin both affected and unaffected by caries through high-performance liquid chromatography (HPLC) at two time intervals. Materials and Methods: Ten freshly extracted restoration-free, caries-free and ten extracted carious human third molar teeth were used in this study. Standardized box-shaped Class I inlay cavities (6 mm long, 3 mm wide, 2 mm deep) were prepared in all teeth with a high-speed handpiece mounted on a standard cavity machine. In teeth affected by caries, after preparation, the remaining carious lesions were removed, with their removal guided by a proprietary caries detector dye. The remaining dentin thickness (RDT) between the pulpal wall of the cavity and the roof of the pulp chamber was measured at multiple points for each tooth so that groups of 10 teeth each were prepared with RDT 1.2 +/- 0.5 mm. Lithium disilicate-based ceramic inlays were manufactured to restore the prepared cavities. A polypropylene chamber was attached to the cementoenamel junction of each tooth to contain 1 ml distilled water. Then, ceramic inlays were cemented with chemically polymerized resin cement (Multilink Automix) according to the manufacturer's instructions. Water elutes were analyzed by HPLC at 4.32 minutes and 24 hours. HEMA diffusion amounts were analyzed using two-way ANOVA and Tukey HSD tests (p < 0.05). Results: HEMA was detected in the pulp chamber elutes of all the teeth. The diffused HEMA amounts were not significantly different between the affected caries and the unaffected groups (p= 0.80) or between time periods (p= 0.44). The carious dentin did not influence the amount of HEMA diffused through the dentin to the pulp space. Conclusions: The highest amount of eluted HEMA concentration detected was not viewed as critical for pulp tissue since the diffused HEMA amounts were below the level of cytotoxicity, according to the literature.