PURPOSE: This study assessed the relationship between changes in autonomic nervous system activity during impacted mandibular third molar extraction and a patient's postoperative psychological status, with the overarching aim of informing the development of interventions to reduce dental phobia and anxiety. We hypothesized that changes in autonomic nervous system activity during tooth extraction are related to postoperative psychology. METHODS: In our prospective cohort study, heart rate variability, heart rate (HR), and systolic blood pressure (SBP) were recorded during impacted mandibular third molar extraction. Heart rate variability values were dichotomized as either low frequency (LF 0.04-0.15 Hz) or high frequency (HF >0.15 Hz). The relative ratios (intraoperative vs baseline) of LF/HF, HF, HR, and SBP were divided into high and low groups based on their median values; the State Anxiety Inventory (STAI-S) results were compared between the groups with high and low relative ratios. RESULTS: Data of 34 female patients (age, 28.23 ± 1.05 years) were analyzed. Postoperative STAI-S values were significantly lower than preoperative values. Patients in the high LF/HF group had a significantly lower change in STAI-S values than those in the low LF/HF group (P < .05). There were no significant differences in the change in STAI-S values between the groups with high and low HF, HR, or SBP. CONCLUSIONS: Patients with low sympathetic nervous system activity had lower anxiety; the LF/HF index was the most sensitive indicator for changes in stress. Additional studies are required to develop optimal interventions for reducing sympathetic nerve activity in patients with dental phobia.